Born in Saint-Alexis on 22 September 1931, Mailhot studied at the Séminaire de Joliette. He earned a master's degree from the Université de Montréal and a doctorate from the University of Grenoble. He began teaching at the Université de Montréal in 1963. He was an editor at the journal "Études françaises" from 1979 to 1987.