Harcourt was born in Oxfordshire, the son of Hon. Simon Harcourt, M.P. for Wallingford and Abingdon, and Elizabeth Evelyn, sister of Sir John Evelyn, 1st Baronet. His father died in 1720, when Simon still a small child. He was educated at Westminster School and in 1727 succeeded his grandfather Simon Harcourt, 1st Viscount Harcourt as 2nd Viscount Harcourt. In 1745, having raised a regiment for service during the Jacobite Rebellion, the 76th Foot (Lord Harcourts Regiment), he received a commission as a colonel in the army. The regiment was disbanded on 10 June 1746.