 Brault-Guillard was raised in Montreal until the age of seven before relocating to France.As a youth, he spent time with Lagnieu and Ain Sud, in the Auvergne-Rhône-Alpes region, before entering the Olympique Lyonnais academy with the under-13 team.In February 2019, Brault-Guillard joined the Montreal Impact on loan from Olympique Lyonnais.