Odilon Desmarais, KC (February 27, 1854 – May 18, 1904) was a lawyer, judge and political figure in Quebec.

He represented Saint-Hyacinthe in the Legislative Assembly of Quebec from 1890 to 1892 and St. James in the House of Commons of Canada from 1896 to 1901 as a Liberal.

Desmarais articled in law with Alexandre Lacoste, was called to the Quebec bar in 1876 and practised in Saint-Hyacinthe with Honoré Mercier and in Montreal.

Desmarais contributed to the newspapers L'Industrie de Trois-Rivières and Le National of Montreal.

Desmarais resigned his seat in the House of Commons after he was named judge for Trois-Rivières district in 1901.