He enlisted in the British Army in 1745 and served during the Seven Years' War. He was at the siege of Louisburg and became an aide-de-camp to General Jeffrey Amherst in 1759 participating in the capture of Montreal. Prescott then served in the West Indies and became Governor of Martinique in 1794.
In 1796 he became governor-in-chief of British North America and commander of British forces. He remained in the position until 1807 but spent much of his time outside of Canada. He was unable to resolve growing demands among French-Canadians and was recalled in 1799.
Prescott, Ontario and Prescott County are named in his honour.