He was born in Paris, the son of Louis Aimé Buffet (1821–1900), who was Inspector General of Bridges and Highways and Marie Anne Philippine Fliche (1840–1921).
Before attending the Académie Julian he was a pupil of Franck Bail (1858–1924) and later of William Laparra (1873–1920), Paul Albert Laurens, Jean-Pierre Laurens (1875–1932) and Henri Royer.
Étienne Buffet exhibited at the Salon des artistes français from 1903 until 1944.
He was appointed "sociétaire" in 1910 and received an "honourable mention" in 1938 for the painting Lecture.
He wrote "Essai de théorie intégrale de la peinture, la doctrine" which approached painting from a mathematician's viewpoint.