Field-Marshal Henry Seymour Conway was second son of Francis Seymour, first Lord Conway, by his third wife, Charlotte the daughter of Sir John Shorter, Lord Mayor of London, and sister of Catherine, wife of Sir Robert Walpole, Earl of Oxford. He was born in 1721 and entered the army at an early age. During the Spring of 1740, he was in Paris, and spent the Summer of that year in London, applying himself diligently to the study of mathematics, fortification and drawing.

The projected marriage, which took place in May 1741, of his brother, Francis Seymour Conway, afterwards Earl and Marquis of Hertford, to Isabella the daughter of Charles, second Duke of Grafton, led to a negotiation for his return as member for the Duke's borough of Thetford. This came to nought and, on 19th October 1741, Conway was returned to the Irish parliament as member for Antrim. On 28th December, however, he was returned to the Parliament of Great Britain as member for Higham Ferrers in Northamptonshire and, with the exception of ten mouths (1774-5), sat in successive parliaments until the dissolution in 1784. He was returned for Penryn, Cornwall, 1st July 1747; for St. Mawes, in the same county, 19th April 1754; for Thetford, Norfolk, 28 April 1731; and for Bury St. Edmunds, Suffolk, 27 March 1775 and 12th September 1780, in each case representing a close constituency.

In 1741, Conway was promoted to Captain-Lieutenant of the 1st Regiment of Foot-Guards, with the rank of Lieutenant-Colonel, and, in the Spring of the following year, joined the army in Flanders. Greatly to his disgust, he found himself condemned to inactivity and spent the Summer at Ghent, employing himself better than his brother officers, generally by reading "both morning and evening". As the States refused to allow their troops to march with the British to the Rhine, Conway, in common with all other officers who were members of parliament, received leave to return to England for the session which opened in November, and formed one of the majority against a vote for disbanding the army in Flanders. In May 1743, he rejoined his regiment near Frankfurt and was present at the battle of Dettingen on 27th June; but, much to his mortification, the brigade of guards was hindered by Baron Ilton, the Hanoverian general, from taking part in the engagement.

Conway returned to England and attended Parliament in the Autumn. Early the next year, he obtained the appointment of aide-de-camp to Marshal Wade, who succeeded Lord Stair in the command of the army in Germany and, in May, joined the marshal at Ghent. The campaign of 1744 was inglorious and Conway returned to England disheartened. He was, at this time, in love with Lady Caroline FitzRoy (the Lady Petersham and Countess of Harrington of Walpole's Letters), the sister of his brother's wife, but his means were small and Horace Walpole persuaded him not to make her an offer.

Between Conway and Walpole, there existed a strong and lifelong attachment and Conway figures largely both in the correspondence and memoirs of his cousin. He was by no means so remarkable a man as Walpole makes him out however. His personal advantages were great. He was singularly handsome, his voice was sweet and his manner, though reserved, was gracious. No man of his time was so generally liked. While he was a man of fashion, his tastes were cultivated and his habits respectable. In a period marked by political intrigue and corruption, he was conspicuous for integrity and a delicate sense of honour. His talents were not brilliant. He lacked decision and insight and he was easily swayed both by his emotions and his friends. He had not the ability either to form or carry out a plan for himself and he unconsciously allowed Walpole to use him as a means of gratifying his spite and his caprices. Of his personal courage, there is no doubt. He was a better soldier than he was a general, a better general than a statesman.

When, in 1745, the Duke of Cumberland replaced Wade in the command of the army in Germany, he appointed Conway as one of his aides-de-camp. The appointment had some influence on his political life. Discontented with the way in which the war was carried on, he had provoked the King and the Duke by some votes he had given on the subject. The renewal of activity delighted him. He became a chief favourite with the Duke and defended the war on all occasions. He joined the army just in time to take part in the Battle of Fontenoy, on 11th May, where he distinguished himself by his personal bravery. In the Autumn, he accompanied the Duke to the north, received the command of the 48th Regiment of Foot on 6th April 1746 and, on the 16th, took part in the Battle of Culloden. He served with the Duke in Flanders, in 1747, and was present at the defeat of the allied army at Lauffeld, in front of Maestricht, on 2nd July. Here, he was overpowered, and barely escaped being stabbed, when on the ground, by a French hussar. He was made a prisoner, but was released on parole.

Conway returned home and, on 19th December, married Caroline the widow of Charles, Earl of Aylesbury, and daughter of Lieutenant-General John Campbell, afterwards Duke of Argyll. Together, they had one daughter, Anne Seymour, who married John Damer, son of Lord Milton, afterwards Earl of Dorchester. On 24th July 1749, he received the command of the 29th Regiment. After his marriage, he lived at Latimers in Buckinghamshire, which he rented for three years. In August 1751, he was ordered to join his regiment in Minorca and visited Italy on his way. Receiving the command of the 13th Regiment of Dragoons in December, he returned home early the next year and bought Park Place at Remenham in Berkshire. He had scarcely had time to settle there before he was ordered to Ireland. Thither Lady Aylesbury accompanied him, leaving her daughter, then three years old, in charge of Horace Walpole. The couple were quartered at Sligo, and returned home in the Summer of 1753, in which year he received a legacy of £5,000, as joint-heir of his uncle, Captain Erasmus Shorter. In 1754, he seconded the address to the Crown and took some part in debates on military matters. On the appointment of Lord Hartington, afterwards Duke of Devonshire, to the Lord-Lieutenancy of Ireland, he insisted on having Conway as secretary. Conway went to Ireland in March, and his conciliatory temper did much towards the pacification of the country. His tenure of office came to an end the following year. Although the place was one of great profit, he was a loser by the employment, for his expenses were large and he did not have the opportunity of reimbursing himself by the second or 'fallow' year, during which, as a matter of course, both the Lord-Lieutenant and the Secretary absented themselves.

Conway's association with the Duke of Devonshire continued after his return to England and, in the Autumn of 1756, Walpole employed him to use his influence with the Duke to accept the Treasury without conditions and allow Pitt full liberty of action in the formation of the ministry. Conway was successful in this endeavour and, thus on 3rd November, defeated a alliance formed by Fox and the Bedford party. In Parliament, Conway was in constant rivalry with Lord George Sackville. His desire to smooth matters over is illustrated by the proposal he made, on 26th February 1757, in the course of the debate on the breach of privilege contained in the King's message on Admiral Byng's case. He suggested that it was not necessary to enter the whole message in the journals of the House, a course which the speaker refused to adopt. In April, he received the appointment of Groom of the Bedchamber.

In the Summer, Conway, who had been promoted to Major-General in the January of the previous year, was summoned from Dorsetshire, where he was with his regiment and, in conjunction with Sir John Mordauut, received the command of an expedition, planned by Pitt, which was to surprise Rochfort and burn the ships in the Charente. Pitt, at first, intended to give Conway the sole command but the King considered that he was too young. Although he thought badly of the plan, he accepted the command and the expedition sailed on 8th September. The fleet was under Sir Edward Hawke, with Knowles, Howe and Rodney, while Cornwallis and Wolfe held military commands. On 20th, the ships appeared off Oleron and, after some debate, the little island of Aix was reduced on the 22nd. Conway then proposed to advance up the river and attack Rochfort. A council of war was held and it was decided that it was impracticable to take the town by surprise. Unwilling to accomplish nothing, he then proposed to attack Fouras, in the hope of being able to burn the French ships and magazines. Some days were wasted, and then an attack was made which failed. Conway wished to renew it and Mordaunt offered to agree if he would take the sole responsibility. This he would not do, though he was willing to make the attempt if one of the other officers in command would advise him to do so. At last, Hawke declared that he would not keep his ships longer at sea at that season and the expedition set sail on the 29th, arriving in England on 3rd October without having done anything.

Great indignation was felt at this failure. Military men generally blamed the plan of the expedition. The ministers and the public blamed its commanders. A court of inquiry was held, which reported that no sufficient ground existed for abandoning the enterprise. Conway's conduct was allowed to pass and a court-martial, held on Mordaunt, ended in an acquittal. In the course of the expedition, Conway showed considerable indifference to personal danger. Associated, however, as he was with Mordaunt, whose powers were shattered by ill-health, his indecision was fatal. Nor was he altogether fitted in other ways for an enterprise of this sort, for his shy and reserved manner prevented his subordinate officers from feeling any enthusiasm for him and he is accused by his detractors of having learned from the Duke of Cumberland to be a martinet to his men. The King received him coldly and struck his name out of the list of the staff; and Pitt was indignant with him. Lord George Sackville made the worst of the matter, an ill-turn which Conway was too generous to repay when Lord George himself fell into far deeper disgrace. The question was debated in pamphlets entitled 'Military Arguments . . . fully considered by an Officer', 'Reply of the Country Gentleman, by Thomas Potter' and 'The Officer's Answer to the Reply', all in 1758, the 'Officer' probably being Conway himself. In consequence of the failure of the Rochfort expedition, he failed in obtaining a command in America, and when Ligonier told the King how eager he was for employment, adding that "he had tried to do something," George answered, "Yes, apres diner la moutarde".

Although Conway was restored to the staff, being promoted to Lieutenant-General on 30th March 1759 and receiving the command of the 1st or Royal Regiment of Dragoons on 5th September following, he was not allowed to go on active service until March 1701, when he was sent to join the British army serving with Prince Ferdinand of Brunswick. On 16th June, the Prince occupied a strong position near the village of Kirch-Denkern, his centre being commanded by Conway and his left by the Marquis of Granby, when Granby's wing was attacked first by De Broglie and, the next day, by Soubise. The French were repulsed with heavy loss. On Granby's return to England, Conway was left in charge of the English army and took up his Winter quarters at Osnaburg, where he was joined by his wife. Early the next Summer, he gained some credit by taking the Castle of Waldeck by stratagem and, on the conclusion of the Peace of Paris, signed on 10th February 1703, brought back the army to England.

When Conway returned, he found Grenville's Government engaged in their attempt to crush Wilkes and, though he did not formally join any party of opposition, he acted with the whigs in resisting the arbitrary measures adopted by the ministers. His conduct enraged George III who, as early as 10th November, proposed to Grenville that he should be dismissed from all his civil and military employments. Grenville hesitated and advised the King to wait until the Christmas recess. On the 24th, Conway voted against the Government on the question of Wilkes' privilege. In the hope of smoothing matters over and keeping him from joining the opposition, Grenville arranged a meeting with him on 4th December, which, by Conway's demand, took place in the presence of the Duke of Richmond. Conway refused to give any pledge of support to the Government and, on 14th and 17th February, spoke and voted against the legality of 'general warrants.' For this offence, the King and the minister not only dismissed him from his post in the household, but deprived him of his regiment. Other officers were treated in the same high-handed fashion. Conway's dismissal was not made known until the House rose in April. The loss of income caused him considerable inconvenience. Walpole at once offered him £6,000 and, shortly afterwards, the Duke of Devonshire wished him to accept £1,000 a year until he was restored to his command. He refused both offers and the Duke, who died shortly afterwards, left him a legacy of £5,000. The case for the Government appears to have been stated in an 'Address to the Public on the Dismission of a General Officer' in the 'Gazetteer' of 9th May. This was answered, though without much ability, by Horace Walpole in 'A Counter-Address', published 12th August, which called forth a singularly poor answer entitled 'A Reply to the Counter-Address', all in 1764. The case roused a determined spirit of resistance in the whigs and Lord Rockingham went down to Hayes in the hope of inducing Pitt to take part in this opposition. Pitt condemned the dismissal, but "considered the question touched too near upon prerogative".

On 8th July 1765, the King was forced to accept the administration formed by the Marquis of Rockingham, in which Conway was Secretary of State, in conjunction with the Duke of Grafton, and Leader of the House of Commons. Conway accepted office somewhat unwillingly at the command of the Duke of Cumberland. He took the southern department and employed William Burke as his private secretary. The accession of the Rockingham ministry to office "abolished the dangerous and unconstitutional practice of removing military officers for their votes in parliament". In order to allay the irritation of the American colonies, the Government determined on the repeal of the Stamp Act, seeking, at the same time, to save the honour of the country by an act declaratory of the rights of Parliament. Conway moved the repeal in February 1766 and, in spite of the intrigues of the King and the opposition of the late ministry, succeeded in gaining a majority. Referring to his triumph on this occasion, Burke in after years said, "I stood near him and his face, to use the expression of the scriptures of the first martyr, his face was as it were the face of an angel". On every account, the King disliked the Rockingham administration and, on 7th July, he acquainted the ministers severally that he had sent for Pitt. On the 13th Pitt, who had undertaken to form an administration with Grafton as First Lord of the Treasury and himself as Lord Privy Seal, with the title of the Earl of Chatham, offered Conway the post of Secretary of State with the Leadership of the House. The Duke of Richmond tried to dissuade him from accepting the offer. The strength of the Rockingham whigs, such as it was, consisted to no small extent in the fact that their party was founded on a strict aristocratic alliance and this the king and Pitt, each from a different motive, were determined to break. The Duke pointed out that Conway's acceptance would further this design and represented that he ought not to desert the Cavendishes, hinting at the obligation he was under to the late Duke of Devonshire. On the other hand, it was probable that, if he refused, the Leadership of the House would go to Grenville and, to prevent this, Walpole urged him to accept. He agreed to do so and, in common with seven others of Rockingham's followers, continued in office under the new administration.

Conway's conduct cannot be judged by the unwritten laws which regulate the party polities of the present day. The question presented to him was not one of measures and the separation between the whig sections was, as yet, rather a matter of cabal than of party. Rockingham appears to have felt some soreness, not so much at Conway's acceptance, but because he did not consider that he made a stand for his followers, many of whom, like himself, were displaced by Chatham, Conway was still held to belong to the Rockingham whigs and formed "the connecting link between the two parties". He soon grew discontented with the violent measures adopted by Chatham for "the breaking-up of parties" and especially at the dismissal of Lord Edgcumbe, one of the old whigs who had four boroughs at his disposal, from the Treasurership of the Household and, in November, had an interview with Rockingham on the subject. Rockingham pointed out that it was evident that Chatham disregarded Conway's "public honour to his party" and even his private honour to his friend, and urged him to resign. The Duke of Portland and four other members of the late Government threw up their places. Unfortunately for his character, Conway, though "very uneasy, perplexed himself with his refinements" and stayed in. All intercourse between him and Chatham now ceased.

A vague project is said to have been concocted, by the King and Lord Hertford,  in January 1767 for placing Conway at the head of a reformed administration. "True to the principles he had uphold under Rockingham," Conway was in favour of lenient measures towards the American colonies and, on 13th March, stood alone in resisting the scheme of the Government for suspending the legislative powers of the New York assembly; but he was powerless to check Townshend's headlong policy and, as he still held office, was forced to follow the administration. He also objected to Chatham's oppression of the East India Company, holding that they had a right to their conquests. At last, on 30th May, he signified, to the King, his wish to retire from office "without any view of entering into faction". The King, however, persuaded him, at least, to delay his resignation. In the preceding year, Conway, in compliance with a request from David Hume, had procured a pension of £100 a year for Rousseau, who was then settled at Wooton in Derbyshire and, when Burke ceased to be his secretary, he gave the place to Hume. In July, negotiations were entered into between Rockingham and Bedford for a union, but were broken off because the Marquis insisted on the condition that Conway should be the Leader of the Commons and, to this, Bedford and Rigby refused to agree. Rockingham's hopes were disappointed and, in January 1708, the Bedford party joined the Government. This put an end to Conway's long-continued state of indecision and he resigned his office on 20th January.

Conway now returned to military life, which was far more to his taste than political office. He had been appointed Lieutenant-General of Ordnance, on 8th September 1767, and as he drew the income of that office as well as full colonel's pay, he had refused the salary of Secretary of State from the date of his appointment, because he was afraid that the Rockingham party might accuse him of remaining in the administration from interested motives. In February 1768, he received the command of the 4th Regiment of Dragoons and took active steps to secure the preservation of peace and the safety of the Royal palace during the Wilkes riots. When, for political reasons, Lord Granby resigned the post of Master of the Ordnance in 1770, the King offered it to Conway. As, however, he too felt dissatisfied with the Government, he refused it, adding that "he would take none of Lord Granby's spoils". He took great interest in his work at the ordnance and effected large economic reforms in the department. To his great annoyance, he found that George Townshend, who retired from the Lord-Lieutenancy of Ireland in 1772, was to be appointed Master-General, and he refused to serve under him. In the debate on the Royal Marriage Act in March of this year, he had annoyed the King by declaring that, though he approved the principle of the bill, he believed that the Crown claimed too much. He attacked the bill in committee and offended Lord North, who was then Prime Minister, by his remarks. The King remonstrated with Lord Hertford on his brother's course and, as Conway considered that his brother tried to dictate to him on the matter, he became more determined. Nevertheless, he could ill spare the pay he received as Lieutenant-General of Ordnance, and Walpole interfered on his behalf. The King was mollified by being told that Conway would not visit the Duke and Duchess of Gloucester and, on his resignation of his post, appointed him Governor and Captain of the Isle of Jersey, on 21st October, an appointment worth about £1,200 a year.

During the Summer of 1774, Conway, who had been promoted to General on 20th May 1772, made a tour of the Continent for the purpose of witnessing the Prussian and Austrian annual reviews. He was accompanied, though they frequently parted company, by Sir Robert Murray Keith, minister at Dresden. At Brunswick, he was kindly received by his old Commander Ferdinand; he visited the divorced Queen of Denmark, King George's sister, at Zell; was entertained at Potsdam by Marischal Keith; and had "a most flattering gracious audience" from the King. He then visited the Austrian camp and the gold and silver mines of Chemnitz and, at the end of August, came through Vienna to the Prussian camp at Schmelwitz near Breslau. He reached Paris in October and spent the Winter there, with his wife and his daughter, Mrs. Damer. During his absence from England, in October 1774, he received the command of the Royal Regiment of Horse Guards.

At the general election, held in November, the Duke of Grafton deprived Conway of his seat for Thetford and he remained out of Parliament until a seat was found for him at Bury St. Edmunds, vacant by the succession of Lord Augustus Hervey to the Earldom of Bristol. On his return to Parliament, he opposed the policy pursued by the Government towards the American colonies. He voted against the address on the ground that it approved of the war and spoke against the bill for restraining trade with the southern colonies. In July 1776, he was laid up with an attack of facial paralysis. This was partly brought on by domestic trouble. His daughter's marriage, in 1767, had greatly pleased him - it was a grand match, for Mr. Damer's father, Lord Milton, was very rich. Mr. and Mrs. Damer received an income of £5,000 a year, the settlements were £22,000, and Conway settled £10,000, the whole of his fortune, upon his daughter. In spite, however, of this provision, the Damers had incurred debts to the amount of £70,000. Conway's attack, however, passed off without leaving any ill effects.

From 1778 to 1781, General Conway was constantly engaged in the affairs of Jersey, staying there four or even seven months in one year. This was rendered necessary by the war with France for, in May 1779 and January 1781, the island was invaded. On hearing of the second invasion, Conway at once sailed from Portsmouth and encountered a violent storm, which occasioned the loss of a transport with sixty men and obliged him, after two days' beating about in the Channel, to put into Plymouth. There, he heard of the defeat of the invasion and returned home, where he was laid up with a severe illness brought on by exposure. Before he had recovered, he received peremptory letters from Lord Hillsborough implying that he was loitering, and treating his absence from Jersey as a matter of leave. This caused him considerable annoyance, and Lord Hertford interfered on his behalf, for the office was not residentiary. The successful defence of the island was due, to some extent at least, to the preparations he had made. He was exceedingly popular with the inhabitants and, some years later, the council presented him with a Neolithic burial chamber or 'Druidic Temple' that had been discovered there, with an inscription in French verse praising his watchfulness and military skill.

Meanwhile, as the war with America, which he had consistently opposed, grew constantly more disastrous for the British army, Conway began to take a prominent part in the attacks made on North's administration. On 5th May 1780, in bringing forward a bill for the pacification of the colonies, he reflected severely on the conduct of the bishops who supported a policy that entailed useless bloodshed. In the course of this Summer, the King is said to have proposed that he should undertake the reconstruction of the Government, entering as Commander-in-Chief, and retaining certain members of the existing administration. The scheme was wholly impracticable and it is doubtful whether the proposal was made with full authority. On 14th December 1781, Conway made a spirited attack on the mismanagement of the Government which had reduced the British to the necessity of peace. Wraxall, in noticing the speeches he delivered at this period, says that "his enunciation was embarrassed and involved"; while they certainly do not evince any particular power of oratory, they read well and clearly. On 22nd February following, Conway moved an address urging the King to renounce any further attempts to reduce America by force, in the course of which he made a vigorous attack on Welbore Ellis, the new Colonial Secretary. "The effect of his speech," Walpole says, "was incredible." On the division, the ministers were left with a majority of only one. He renewed the attack on the 27th, and taunted Dundas and Rigby with possessing the "gift of tongues - double tongues." He was now "completely master of the deliberations of the house on the subject of America," and, on 4th March, gained another victory.

On the 20th, North at last obtained permission to resign. In the ministry formed by Rockingham, which entered office on the 27th, Conway was commander-in-chief with a seat, in the cabinet. It was formed out. of a combination of the parties of Rockingham and of Shelburne, who was a Secretary of State. When Buckingham died, on 1st July following, the King made Shelburne Prime Minister. Fox, Burke and some others resigned; Conway, the Duke of Richmond, and other members of the party retained their offices. Although it has been stated that some jarring took place on account of Shelburne's refusal to accede to the wish of Conway and Pitt, that Fox should be brought into the cabinet, it is certain that Shelburne would have admitted him, and that Fox absolutely refused to act with him. On 9th July, Conway defended the Government from the attacks of Fox, denying that there was any division in the Cabinet or any departure from its original policy in the matter of the peace. Burke ridiculed him for serving under Shelburne, declaring that he was like Little Red Riding Hood, who "didn't know a wolf from her grandmother." He disliked the treaties with France and Spain, and was not altogether easy in the Cabinet, especially after the retirement of Keppel in January 1783. The ministry resigned on 24th February following.

During the prolonged crisis that ensued on Pitt's acceptance of office, Conway, ever swayed by those around him, was infected by the prevailing violence. On the defeat of Pitt's East India Bill in January 1784, he taunted the minister with his silence, pressed him to state his intentions, declared that the conduct of the Government was corrupt and, on 1st March, supported Fox's motion for an address to the Crown for Pitt's dismissal. Parliament was dissolved, on 25th, and Conway's political life ended. He resigned his military command and retired to Park Place, keeping his Governorship and occasionally visiting Jersey.

The remainder of Conway's life was pleasantly spent. He enjoyed the beauty of his country retreat, where, among other pursuits, he propagated trees, raising poplars from a cutting brought from Lombardy by Lord Rochford. In 1778, he gave Crabbe, the poet, a work on botany, along with other books: all through his life he appears to have been friendly with men of genius. His taste was good and he has left an enduring monument of it in the bridge at Henley-on-Thames (Oxfordshire), about which he was busied in 1787. Before his retirement, he invented a furnace for the use of brewers and distillers, for which he afterwards took out a patent.

Part of the leisure of his last years was, moreover, devoted to literary work. In 1789, he sent Walpole a tale which his friend described as "very easy and genteel" - it was evidently in verse. He wrote and printed a prologue to the play 'The Way to keep him,' acted by amateurs at the private theatre at Richmond House, in April 1787, and "altered from the French," the original being 'Dehors Trompeurs' of Louis de Boissy, a comedy entitled 'False Appearances,' which was first performed at Richmond House, and then published in 1789 with a long dedication to Miss Farren, who acted in it at Drury Lane. The prologue is by the author, the epilogue by Lieutenant-General Burgoyne. Conway's pamphlets in defence of his conduct of the Rochfort expedition have been already noticed. His speech on American affairs, delivered on 5th May 1780, was published separately in 1781. Several of his private letters to Walpole from 1740 to 1746 are in an appendix to the 'Rockingham Memoirs';  two or three of later dates are included in the 'Letters' of Horace Walpole, and some extracts of letters written from Germany in 1774 are in Carlyle's 'Frederick the Great'.

On 12th October 1793, Conway was appointed Field-Marshal. He died at Park Place in Remenham on 12th October 1795, in his seventy-fifth year.