Saint-Firmin (; ) is a commune in the Hautes-Alpes department in southeastern France.
Saint-Firmin has an oceanic climate (Köppen climate classification Cfb). The average annual temperature in Saint-Firmin is . The average annual rainfall is with October as the wettest month. The temperatures are highest on average in July, at around , and lowest in January, at around . The highest temperature ever recorded in Saint-Firmin was on 19 August 2012; the coldest temperature ever recorded was on 27 December 1962.