Prévost was a Swiss born British Army officer. During the Seven Years War, Prévost was commissioned as a major in the 60th (Royal American) Regiment of Foot. The 60th was raised in North America, included many foreign and colonial Protestants, and was designed to utilize the forest tactics prevalent in North America. By the outbreak of the American Revolution, Prévost was a colonel with the 60th, stationed in St. Augustine Florida. In 1778, Prévost was ordered to invade Georgia, arriving in Savannah in January of 1779, taking command of all British forces there with the rank of brigadier general. Prévost, however, felt that he was too old for combat and asked to resign. He was replaced by General George Garth, who was captured before reaching Savannah leaving Prévost in command with the rank of major general. Prévost was in command for the Siege of Savannah, returning to England after the British victory. His son later served as both a general and royal governor in Canada in the War of 1812.