The son of a farmer fascinated by trains, Auguste Forestier ran away from home frequently during his adolescence. Regularly returned to his family, he was first committed to the Saint-Alban psychiatric hospital from 1906 to 1912. In 1914, he was permanently committed after derailing a train by placing stones on the track.

A medical certificate from 1915 notes that he drew a great deal and sculpted butcher's bones. His thirst for freedom, however, never left him, and between 1914 and 1923, he escaped five times.

Around 1930, he began making toys and wooden figurines dressed in recycled materials. He was discovered by Paul Éluard in 1943, when the latter, fleeing Paris, had taken refuge in Lozère with his wife.

Returning to Paris in 1944, he brought back three sculptures by Forestier and showed them to Picasso and Queneau. Dubuffet, who had not yet coined the term "art brut," also discovered Forestier at Éluard's. It was following this initial encounter that Dubuffet went to Saint-Alban.