Born at Penne, Sarrazin joined the dragoons at sixteen and was rapidly promoted after 1792. He became adjutant-general of the Army of Sambre-et-Meuse in Italy in 1794, and was promoted to the rank of brigadier on 23 August 1798. He was a leader of the French expedition to support the Irish rebels in 1798, and distinguished himself at the Battle of Castlebar. Although intelligent and brave, his career was several times set back by his irascibility and vanity.