Nathaniel Fiennes (c. 1608 – 16 December 1669) was a younger son of the Puritan nobleman and politician, William Fiennes, 1st Viscount Saye and Sele. He sat in the House of Commons at various times between 1640 and 1659, and served with the Parliamentarian army in the First English Civil War. In 1643, he was dismissed from the army for alleged incompetence after surrendering Bristol and sentenced to death before being pardoned. Exonerated in 1645, he actively supported Oliver Cromwell during The Protectorate, being Lord Keeper of the Great Seal from 1655 to 1659.