Anne was the eldest daughter of the Lord Protector of England, Edward Seymour, the Duke of Somerset by his second wife, Anne, the daughter of Sir Edward Stanhope of Rampton in Nottinghamshire. She was also first cousin to King Edward VI. Anne would have grown up partly at Wolf Hall at Great Bedwyn in Wiltshire, but mostly at the Royal Court and at Somerset House on the Strand.

The tutor of Anne, Margaret and Jane, the Duke of Somerset's three eldest daughters, was a Frenchman named Nicholas Denisot. He taught them Latin, Greek, Italian and French, as well other important academic subjects of the age usually reserved for boys. A poetical tribute to the memory of Margaret Queen of Navarre, written in Latin (and translated into the three other languages) has been attributed to these three sisters - of course under the guidance of their tutor. It was printed after Denisot's return to Paris in 1551, under the title “The Grave of Margaret of Valois, Queen of Navarre”. They are further said to have been complimented as “three beautiful singers” in one of the odes of Ronsard and Anne was certainly known for her religious studies, having even corresponded with John Calvin.

The lady’s first marriage is one of the most memorable ever made by a subject in England, from its connection with the great events of Tudor history. It formed the reciprocal exchange of hostages, when a peace (or rather a truce) was concluded between the Duke of Somerset and his great rival for power, the Earl of Warwick (later Duke of Northumberland), after the first political attack made upon the former in 1549. Though, like other alliances spun by hollow politicians, it proved a very inefficient and frail check upon the jealousy and ambition of the parents of the contracting parties.

The marriage of Lady Anne to Warwick’s eldest son, John Dudley, Viscount Lisle, was solemnised at the Royal palace of Sheen, on 3rd June 1549. She was eleven. He was twenty-two. The fourteen-year-old King Edward sanctioned, by his presence there, the pacification of his rival ministers and the bestowal of the hand of his fair cousin. The following is the account of the occurrence which was entered by the youthful monarch in his diary, showing that his mind was chiefly occupied with the festivities which graced the occasion:

“1549, June 3: The King came to Sheen, where was a marriage made between the Lord Lisle, the Earl of Warwick’s son, and the Lady Anne, daughter to the Duke of Somerset; which done and a fair dinner made and dancing finished, the King and the ladies went into two chambers made of bows where first he saw six gentlemen of one side and six of another run the course of the field twice over. There names here do follow: The Lord Edward and Sir John Appleby. [The other names not inserted.]

Last of all came the Count of Ragonne with 3 Italians, who ran with all the gentlemen four courses, and afterwards fought at tourney. And so after supper, he returned to Westminster [in his barge, by water]. And afterward came three masquers of one side and two of another which ran four courses apiece. Their names be [blank]”

It was on the following day that Sir Robert Dudley, Lord Lisle’s younger brother and afterwards Earl of Leicester, married Sir John Robsart's daughter, Amy, also at Court.

The rejoicings upon John and Anne’s marriage were, however, soon exchanged for tears. In the course of a few weeks, perhaps days, the bride must have witnessed fresh enmity springing up between the families of her husband and her father: which very shortly, in January 1552, brought the latter to the scaffold. Then followed, within two years, the ruin of her husband’s house; the retributive execution of her father-in-law, the Duke of Northumberland; and the imprisonment of his four sons. Following the death of King Edward, Northumberland had failed in his attempt to place the King’s Protestant cousin, Lady Jane Grey, and his own son, Guildford, on the Throne. Anne’s husband, by then the Earl of Warwick, had been arrested, together with his father, on the orders of the Catholic Queen Mary, at Cambridge on 25th July 1553; and arraigned and condemned with him at Westminster on 18th of the following month. After his father’s decapitation, Warwick continued as a prisoner in the Tower of London and, on 10th September, his fifteen-year-old Countess, was given license to visit him and to stay as long and as often as the Lieutenant of the Tower thought convenient. The same permission had, on the preceding day, been granted to her sisters-in-law, the wives of the Lords Ambrose and Robert Dudley.

In the Beauchamp Tower at the Tower of London, on the right-hand side of the fireplace, is a very curious and elaborate carving, cut by the hands of "IOHN DVDLE" and representing his family insignia of a chained bear and lion, supporting between them a ragged staff, within a border of flowers, and with this inscription below:
You that these beasts do well behold and see,
May deem with care wherefore here made they be,
With borders eked wherein [unfinished – possibly are found]
Four brothers names who list to search thee around.
[Two more lines prepared but not sculptured].
The four flowers, or plants, in the border may be interpreted as the jonquil (for John), the rose (for Ambrose), the herb (for Robert) and the Gillyflower (for Guildford).

John, Earl of Warwick and his brothers were released from prison on 18th October 1554. Anne took her husband, already very ill, to Penshurst Place in Kent, the mansion of his brother-in-law, Sir Henry Sydney. He died there on the 28th of the same month, within ten days of his deliverance from prison.

When six months had elapsed - on 29th April 1555 - the Countess, still aged only sixteen or seventeen, entered into a second marriage with Edward Unton (later Sir Edward) of Wadley House at Littleworth in Faringdon, Berkshire. The match was arranged by Unton's step-father, Robert Keilway, an old family friend of the Seymours. It was solemnized in a scene very different to that which had witnessed the former splendid but calamitous alliance of the lady. It took place in the small and sequestered church of Hatford in Berkshire, a short distance from Mr Unton's mansion, probably in secret. A quiet life in the Vale of the White Horse was probably just what Anne needed.

One assumes the marriage was at least reasonably happy, as they had some seven children together. Anne was eventually granted a life share in her former husband's forfeited lands and perhaps, after Queen Elizabeth’s succession in 1559, she may even have enjoyed some reflected glory from her brother-in-law, the Queen’s favourite, Robert Dudley (eventually Earl of Leicester). Her new husband was certainly knighted at the Coronation. However, it may also be supposed that the harassing and tragic events of the Countess’ early years could not be forgotten and eventually unbalanced her mind. She spent a prolonged period alone, while Sir Edward went off on his Italian tour, and by 1566, when the youngest of her children can only have been four at the most, she was declared to be “a lunatic enjoying lucid intervals”. She was only twenty-eight. She apparently continued in this sad state for the next twenty-two years, probably being hidden away at Wadley when Sir Edward entertained the Queen at their Langley home in Oxfordshire. She outlived her husband by six years, eventually dying at Wadley in February 1588, and was buried under her husband’s fine monument in Faringdon Church. It must have been a blessed release for everyone concerned.