Montagu was the son of Sir Edward Montagu, who was a judge, of Boughton, Northamptonshire and grandson of Sir Edward Montagu.
Sidney Poitier | Sidney Lumet | Sidney Nolan | Sidney Bechet | Philip Sidney | John Montagu, 4th Earl of Sandwich | Sidney Crosby | Lady Mary Wortley Montagu | Albert Sidney Johnston | Sidney Herbert, 1st Baron Herbert of Lea | Sidney | Sylvia Sidney | Sidney Reilly | Sidney Altman | John Neville, 1st Marquess of Montagu | Walter Montagu Douglas Scott, 5th Duke of Buccleuch | Sidney Paget | Sidney Howard | Sidney Colvin | Montagu's Harrier | Henry Sidney | George Montagu-Dunk, 2nd Earl of Halifax | Sidney Smith | Sidney Lee | Sidney Godolphin, 1st Earl of Godolphin | Sidney Cotton | Sidney Blumenthal | Montagu Love | Montagu House, Bloomsbury | Montagu House |
He was also the brother of Henry Montagu, later created Earl of Manchester, and of Sidney Montagu, ancestor of the Earls of Sandwich.