Lise St-Denis (born April 18, 1940) is a former Canadian politician. She was elected to the House of Commons of Canada in the 2011 election and served a single term. She was elected in the electoral district of Saint-Maurice—Champlain as a member of the New Democratic Party, but crossed the floor to the Liberal Party of Canada on January 10, 2012, saying in French to explain her move: "Voters voted for Jack Layton. Jack Layton is dead."

Prior to being elected, St-Denis was a teacher. She has bachelor's and master's degrees in Quebec literature and education. She previously ran as the New Democratic Party's candidate in Longueuil—Pierre-Boucher in the 2008 election, losing to Jean Dorion of the Bloc Québécois.

Shortly after her election, St-Denis was diagnosed with non-Hodgkin's lymphoma. She did not stand for re-election in 2015.

Before joining the Liberals, St-Denis supported Thomas Mulcair as the next leader of the NDP.

2011 Canadian federal election
Party	Candidate	Votes	%	±%	Expenditures
	New Democratic	Lise St-Denis	18,628	39.1	+31.3
	Bloc Québécois	Jean-Yves Laforest	13,961	29.3	-14.7
	Conservative	Jacques Grenier	8,447	17.7	-6.2
	Liberal	Yves Tousignant	5,670	11.9	-9.1
	Green	Pierre Audette	972	2.0	-1.4
Total valid votes/Expense limit			47,678	100.0
Total rejected ballots			1,193	2.4	–
Turnout			48,871	60.8	–
Eligible voters			80,315	–	–

2008 Canadian federal election
Party	Candidate	Votes	%	±%	Expenditures
	Bloc Québécois	Jean Dorion	23,118	46.1	-9.1	$49,818
	Liberal	Ryan Hillier	10,920	21.8	+9.2	$10,797
	Conservative	Jacques Bouchard	7,210	14.4	-4.4	$55,552
	New Democratic	Lise St-Denis	7,021	14.0	+5.4	$1,131
	Green	Danielle Moreau	1,752	3.5	-0.5
	Marxist–Leninist	Serge Patenaude	103	0.2	–
Total valid votes/Expense limit			50,124	100.0	$83,504
Total rejected ballots			682	1.34
Turnout			50,806

• Lise St-Denis – Parliament of Canada biography