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 was an unsuccessful candidate for a seat in the provincial assembly in a 1902 by-election.
Mousseau died in Montreal at the age of 90 and was buried in Notre-Dame-des-Neiges Cemetery.