Sir Philip Mainwaring (1589 – 2 August 1661) was an English politician who sat in the House of Commons variously between 1625 and 1661.
Mainwaring was the son of Randall Mainwaring, of Peover, Cheshire. He was admitted at Gray's Inn on 14 March 1609, and matriculated at Cambridge from Brasenose College, Oxford on 29 August 1610. He was awarded BA from Oxford in 1613 and entered Lincoln's Inn on 15 February 1614. In 1624 he was awarded MA at Cambridge on visit of King Charles.
Mainwaring was elected Member of Parliament for Boroughbridge in 1625 and 1626. He was elected MP for Derby in 1628 and sat to 1629 when King Charles decided to rule without parliament for eleven years.
In 1634 Mainwaring became Principal Secretary to the Lord Deputy of Ireland, Lord Strafford. Strafford's biographer refers to him as a "court hanger-on" who was disliked by many of Strafford's friends, but who had provided him with useful intelligence in the past, and who justified the Earl's trust by proving a diligent and loyal official, who remained faithful to his employer.
He was knighted at Dublin Castle on 13 July 1634. He was an MP in the Irish House of Commons for Clonakilty from 1634 to 1635 and for Carysfort from 1640 to 1641.
Mainwaring was elected MP for Morpeth for the Short Parliament in April 1640. He was imprisoned in 1650.