Elected to the Long Parliament in November 1640, Fiennes played a leading role in the opposition to Charles I prior to the outbreak of civil war in August 1642.

In the early years of the war, his objections to any form of established church aligned him with Cromwell and the Independents, rather than the moderate Presbyterians who dominated Parliament.

Following the 1660 Stuart Restoration, he was pardoned under the Indemnity and Oblivion Act, and lived quietly at home in Newton Tony, Wiltshire, until his death on 16 December 1669.

), daughter of Sir John Eliot, an MP who played a leading role in passing the 1628 Petition of Right; he was later imprisoned by Charles I in the Tower of London, where he died in 1632.

[1] They had two surviving sons, Nathaniel (1637–1672), who inherited his fathers' estates, and William (1639–1698), who succeeded his uncle James as Third Viscount Saye and Sele in 1674.

[2] [a] Like his Puritan father, he strongly opposed Laudianism and Episcopacy in any form, opinions strengthened by his residence in the Calvinist stronghold of Geneva.

[3] He spoke against the illegal canons[clarification needed] on 14 December 1640, and again on 9 February 1641 on the occasion of the reception of the Root and Branch petition, when he argued against episcopacy as constituting a political as well as a religious danger and made an impression on the House of Commons, his name being added immediately to the committee appointed to deal with church affairs.

[3] He took a leading part in the examination into the army plot; was one of the commissioners appointed to attend the king to Scotland in August 1641; and was nominated one of the committee of safety[clarification needed] in July 1642.

On the outbreak of hostilities he took arms immediately, commanded a troop of horse in the army of Lord Essex, was present at the relief of Coventry in August, and at the fight at Powick Bridge, Worcester in September, where he distinguished himself, and subsequently at Edgehill.

He addressed to Essex a letter in his defence (Thomason Tracts E. 65, 26), drew up for the parliament a Relation concerning the Surrender ... (1643), answered by William Prynne and Clement Walker accusing him of treachery and cowardice, to which he opposed Col. Fiennes his Reply[clarification needed] ....[3] Dorothy Hazzard a local preacher gave evidence against him.