Benjamin was the son of James Rudyard (sometimes spelt Rudyerd), of Winchfield in Hampshire, by his wife, Margaret, the daughter and heiress of Lawrence Kidwelly of Hartley Wintney in the same county. Lawrence's father was descended from Sir Morgan Kidwelly, Attorney-General to Kings Edward V & Richard III and one of the Kidwellys of Little Wittenham. His mother was one of the Coudrays from Padworth and Herriard. Benjamin was born on 26th December 1572. He was educated at Winchester School and matriculated from St. John's College, Oxford, on 15th January 1588, but does not appear to have graduated. On 18th April, he was admitted to the Inner Temple and, on 24th October 1600, was called to the bar.

Rudyard's career falls naturally into three parts. "His youthful years," says Wood, "were adorned with all kinds of polite learning, his middle years with matters of judgment, and his latter with state affairs and politics". His poems, though not printed till after his death, gained Rudyard considerable reputation as a poet and he was also accepted as a critic of poetry. He was friends with Ben Jonson, John Hoskins, John Owen the epigrammatist and other men of letters, and was on intimate terms with William Herbert, Earl of Pembroke. Jonson printed, in 1616, three epigrams addressed to Rudyard, praising his virtues, his friendship and his "learned muse". Another poem written on seeing Rudyard's portrait is indifferently attributed to John Owen or Sir Henry Wotton. Rudyard's friendship with John Hoskins was interrupted by a duel, in which the former is said to have been wounded in the knee. His intimacy with Pembroke, testified by his answers to Pembroke's poems, was further cemented by his marriage with Elizabeth, the daughter of Sir Henry Harington. She was Pembroke's second cousin. In 1610, Rudyard obtained a license to travel for three years and Lord Herbert of Cherbury mentions meeting him being in Florence in 1614.

After his return, he was knighted, on 30th March 1618, and granted, on 17th April, the post of Surveyor of the Court of Wards for life. Rudyard held this lucrative office until its abolition by the Long Parliament in 1647, when he was voted £6,000 as a compensation for its loss. Rudyard's political career began in 1620, in which year he was returned to Parliament for the borough of Portsmouth. In later parliaments, he represented Portsmouth (1624, 1625), Old Sarum (1626), Downton (1628) and Wilton in the two parliaments of 1640. His earliest speeches combine zeal for the cause of the Elector Palatine with a desire to please King James, and he maintained this moderate attitude throughout the disputes of the next eight years.

In the parliament of 1623, Rudyard came forward as the chosen spokesman of the Government. "His official position as Surveyor of the Court of Wards, together with his close connection with Pembroke, made him a fit exponent of the coalition which had sprung up between [the Duke of] Buckingham and the popular lords". He advocated war with Spain, a confederation with foreign Protestant princes and a liberal contribution to the King's necessities. In the first parliament of Charles I, Rudyard, still following the lead of his patron, Pembroke, played a similar part. He commenced with a panegyric on the virtues of the new sovereign, prophesying that the distaste between Parliament and Sovereign would now be removed, for the King "hath been bred in parliaments, which hath made him not only to know, but to favour the ways of his subjects". Holding these views, he took no part in the attack on the Duke of Buckingham, during the Oxford session, and approved the device of making the opposition leaders sheriffs in order to prevent them renewing the attack in the next parliament. "The rank weeds of parliament," he wrote to a friend, "are rooted up, so that we may expect a plentiful harvest the next". In spite of his disinclination to act against the Government, he was one of the sixteen members appointed to assist the managers of Buckingham's impeachment, on 3rd May 1626, but took no public part in the trial, while showing characteristic zeal for questions of church reform. In 1628, while still endeavouring to mediate, he took a stronger line for redress of parliamentary grievances. "This," he said, "is the crisis of parliaments … If we persevere, the King to draw one way, the Parliament another, the Commonwealth must sink in the midst". He emphatically declared himself against the King's claim to arrest without showing cause, holding that a new law, rather than a mere re-enactment of Magna Carta, was necessary, though professing that he would be glad to see that "good old decrepit law, Magna Carta, walk abroad again with new vigour and lustre". His speech on the liberty of the subject was criticised by William Laud as seditious and this criticism was adduced as evidence against the archbishop at his trial.

During the intermission of parliaments, Rudyard turned his attention to colonial enterprises. He was one of the original incorporators of the Providence Company, on 4th December 1630, and, like other members of the company, sometimes repaired his losses as a coloniser by his gains in privateering. It was probably to his connection with the Providence Company that Rudyard owed his place, from 2nd November 1643, in the council appointed by the Long Parliament for the government of the English Colonies.

In the Short Parliament of April 1640, Rudyard resumed the part of mediator. "If temper and moderation be not used by us, beware of having the race of parliaments rooted out." In the Long Parliament, he created a great impression by the vigorous attack on the King's evil counsellors which he made on the first day of its debates. "Under the name of Puritans," he complained, "all our religion is branded. Whosoever squares his actions by any rule, either divine or human, he is a Puritan. Whoever could be governed by the King's laws, he is a Puritan. He that will not do whatsoever other men would have him do, he is a Puritan". He followed up this speech with an attack on the new canons imposed by the religious synod of 1640, but drew back when the abolition of bishops was proposed, and advocated a limited episcopacy. Rudyard spoke several times against the Earl of Strafford and did not vote against the bill for his attainder. He was a zealous advocate of a vigorous and Protestant foreign policy, and opposed any suggestion to tolerate Catholicism in Ireland. In the debate on the ‘Grand Remonstrance,’ while agreeing with the historical portion of that manifesto, he objected to what he termed the 'prophetical part'. On 9th July 1642, when civil war was imminent, he made a pathetic appeal for peace, which was immediately republished and circulated by the Royalists. Yet, in spite of his repugnance to war, Rudyard did not leave the Long Parliament, though, the fact that his attendance was twice especially ordered, seems to show that he sometimes thought of retiring from Westminster. He took the two covenants, acted as a commissioner for the government of the colonies and was appointed a member of the Assembly of Divines, 12th June 1643. In 1648, he supported the Presbyterians in urging an accommodation with the King, was arrested by the army on 6th December and was, for a few hours, imprisoned. Rudyard took no further part in public affairs and died on his country estate, West Woodhay House in Berkshire, on 31st May 1658. His epitaph, written by himself, is printed by Wood and by Le Neve. Rudyard left one son, William, some verses by whom are prefixed to Lovelace's ‘Lucasta.’