Léonce Mercier (August 11, 1926 – December 27, 2019) was a Canadian Senator from Quebec as well as a businessman and consultant. Mercier is a long-time activist and organizer in the Liberal Party of Canada in Quebec under Pierre Trudeau and Jean Chrétien and Quebec Liberal Party during the leadership of Jean Lesage and Robert Bourassa. He began his involvement in northern Quebec in the Saguenay–Lac-Saint-Jean region. He was director general of the Liberal Party of Quebec from 1978 to 1985.