Joseph-Octave Mousseau (August 2, 1875 – December 2, 1965) was a lawyer and political figure in Quebec. He represented Soulanges in the Legislative Assembly of Quebec from 1904 to 1914 as a Liberal member.He was born in Saint-Polycarpe, Quebec, the son of Joseph-Octave Mousseau and Rose-Avelina Cadieux. Mousseau studied at Collège Bourget at Rigaud and the Université Laval; he was called to the Quebec bar in 1897 and set up practice in Montreal. In 1899, he married Clara Gagné.