Peter Fonseca (born in Lisbon, Portugal in 1966) is a politician in Ontario, Canada. He is currently a member of the Legislative Assembly of Ontario, representing the riding of Mississauga East for the Ontario Liberal Party.

Fonseca was raised in Toronto, Canada, and attended the University of Oregon on an athletic scholarship. He also has a Bachelor of Education degree from the University of Windsor. He represented Canada at the 1996 Olympic Games in Atlanta, Georgia as a marathon runner. He was the top finisher for the Canadians, placing 21st overall in a 26.2 mile race with a time of 2 hours, 17 minutes and 28 seconds. He also placed second in the 1994 Toronto Marathon and the 1994 Houston Marathon , and third in the 1992 New York Marathon and the 1990 Los Angeles Marathon. He is a recipient of the Fred Bagley Memorial Trophy, given to long distance runners in Canada.

Fonseca was later a senior performance management consultant for the Coach Corporation, and has run a successful importing and distributing company in Portugal. He has also done fundraising work for the Canadian Diabetes Association .

Fonseca was elected to the Ontario legislature in the provincial election of 2003, defeating incumbent Progressive Conservative Carl DeFaria by about 3000 votes in Mississauga East. On October 23, 2003, he was named Parliamentary Assistant to Gerard Kennedy, the Minister of Health and Long-Term Care . Fonseca is regarded by many as a rising star in the Liberal Party.