At the outbreak of the French Revolution in 1789, Gazan returned to Grasse and joined the National Guard. In 1790, he became a captain and, in 1791, a lieutenant colonel of the local volunteer battalion of the Var. In 1792, with the declaration of war with Austria, he was sent to the 27th Regiment. His regiment first served garrison duty in Strasbourg, but in December 1793, participated in the Battle of Wissembourg. In May 1794, Gazan became a battalion commander of the new 54th Demi-Brigade. On 4 July, he routed the Prussians in Kuppenheim by ordering his drummers to beat a charge, convincing the Prussians that they were outnumbered. He was promoted to brigade colonel on 11 July and led his troops to victory against the Prussians at Trippstadt.