Educated at Eton College, Stanhope was commissioned in 1703 as a lieutenant in the 2nd Foot Guards during the War of the Spanish Succession, before transferring to the 3rd Foot Guards in Spain. By 1710, he was a lieutenant-colonel and missed the December 1710 Battle of Brihuega, when the British rearguard under his cousin James Stanhope was cut off and forced to surrender. In March 1711, he became Colonel of the former Lepells Regiment, which was disbanded in November 1712 as the army was cut back in the run-up to the 1713 Peace of Utrecht.