Nathaniel Fiennes, the son of William Fiennes, was born in about 1608. In 1640 he was elected to the House of Commons. A close friend of Oliver Cromwell, he supported the Independents against the Presbyterians.

On the outbreak of the Civil War Fiennes supported the Parliamentary army. However, he was disgraced in 1643 when he surrendered Bristol to Prince Rupert.

Fiennes supported negotiations with Charles I and in 1648 was expelled from the House of Commons as a result of Pride's Purge.

In 1654 Fiennes was appointed to the Council of State. He also sat in Cromwell's House of Lords. Nathaniel Fiennes died in 1669.