St. Catharines is a federal electoral district in the Niagara Region of Ontario, Canada, that has been represented in the House of Commons of Canada since 1968.

It consists of the part of the City of St. Catharines lying east and north of a line drawn from Lake Ontario: Courtleigh Road, Third Street Louth, the QEW, Highway 406, First Street Louth, St. Paul Street West, St. Paul Crescent, Twelve Mile Creek, Glendale Avenue, Merrit Street and Glendale Avenue.

It was created in 1966 from parts of Lincoln riding.

It consisted initially of the part of the City of St. Catharines bounded on the east by the eastern city limit, and on the north, west and south by a line drawn from the city limit southwest along Eastchester Avenue, south along Bunting Road, southwest along Rockwood Street, south along Hartzell Road, northwest along the Canadian National Railway (CNR) line, south along Glengarry Road, east along Glendale Avenue, south along Mountain Street and east along Bradley Street to the city limit.

In 1976, it was redefined to consist of the part of the City of St. Catharines lying north of the Canadian National Railway.

In 1987, it was redefined to consist of the part of the City of St. Catharines lying north of a line drawn from west to east along St. Paul Street West, St. Paul Street West to St. Paul Crescent, the old Welland Canal, Carter Creek, the first Canadian National Railway spur line and the main CNR line and Queenston Street.

In 1996, it was redefined to consist of the part of the City of St. Catharines lying north and east of a line drawn from the western city limit along St. Paul Street West, St. Paul Crescent, the Old Welland Canal, Carter Creek, the first Canadian National Railway spur line, the most easterly Canadian National Railway spur line and the yard line to the southern city limit.

In 2003, it was given its current boundaries as described above.

This riding lost fractions of territory to Niagara West and Niagara Centre during the 2012 electoral redistribution.

According to the 2021 Canadian census

Ethnic groups: 80.7% White, 4.2% Black, 3.5% Indigenous, 2.4% Latin American, 2.2% South Asian, 1.4% Filipino, 1.3% Chinese, 1.2% Arab

Languages: 79.9% English, 2.1% Spanish, 1.8% French, 1.4% Italian, 1.3% German, 1.2% Arabic, 1.1% Polish

Religions: 58.3% Christian (25.7% Catholic, 6.1% Anglican, 4.2% United Church, 1.9% Presbyterian, 1.3% Anabaptist, 1.3% Christian Orthodox, 1.2% Baptist, 1.1% Lutheran, 1.1% Pentecostal, 14.4% Other), 3.1% Muslim, 36.2% None

Median income: $37,600 (2020)

Average income: $46,760 (2020)

Riding associations are the local branches of the national political parties:

Party		Association name	CEO	HQ address	HQ city
	Christian Heritage Party of Canada	Christian Heritage Party St. Catharines E.D.A.	Bill Luchies	21 Forster Street	St. Catharines
	Conservative Party of Canada	St. Catharines Conservative Association	Grace Pang	109 Magnolia Lane	Welland
	Liberal Party of Canada	St. Catharines Federal Liberal Association	Margaret Jarrell		St. Catharines
	New Democratic Party	St. Catharines Federal NDP Riding Association	Irene E. Lowell	5 Roehampton Avenue	St. Catharines

This riding has elected the following members of the House of Commons of Canada:

Parliament	Years	Member		Party
St. Catharines Riding created from Lincoln
28th	1968–1972		James McNulty	Liberal
29th	1972–1974		J. Trevor Morgan	Progressive Conservative
30th	1974–1979		Gilbert Parent	Liberal
31st	1979–1980		Joseph Reid	Progressive Conservative
32nd	1980–1984
33rd	1984–1988
34th	1988–1993		Ken Atkinson
35th	1993–1997		Walt Lastewka	Liberal
36th	1997–2000
37th	2000–2004
38th	2004–2006
39th	2006–2008		Rick Dykstra	Conservative
40th	2008–2011
41st	2011–2015
42nd	2015–2019		Chris Bittle	Liberal
43rd	2019–2021
44th	2021–present