Sir Sidney Montagu (died 25 February 1644) was an English politician who sat in the House of Commons at various times between 1593 and 1642. He supported the Royalist cause in the First English Civil War. Montagu was one of the younger of the eight sons of the judge Sir Edward Montagu of Boughton and Elizabeth Harington. He was the grandson of another judge Sir Edward Montagu and his third wife Helen or Eleanor Roper. He matriculated at Christ's College, Cambridge in December 1588 and was admitted at Middle Temple on 11 May 1593.