Fiennes was the third son of the 1st Viscount Saye and Sele. At the outbreak of the English Civil War he joined the Parliamentary side, and rose to the rank of the colonel of a regiment of horse by 1643, and served at the Battle of Naseby.
He was elected to the Long Parliament as member for Morpeth, probably in 1645, but was one of the MPs excluded in Pride's Purge in December 1648. In 1658, he was chosen a member of Cromwell's Upper House.
- Concise Dictionary of National Biography (1930)
- D. Brunton & D. H. Pennington, Members of the Long Parliament (London: George Allen & Unwin, 1954)
- Cobbett's Parliamentary history of England, from the Norman Conquest in 1066 to the year 1803 (London: Thomas Hansard, 1808) 
- Mark Noble, Memoirs of several persons and families... allied to or descended from... the Protectorate-House of Cromwell (Birmingham: Pearson & Rollason, 1784) 
|Parliament of England|
Sir William Carnaby
|Member of Parliament for Morpeth
With: George Fenwick
Not represented in Rump Parliament
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