Sir John A. Macdonald Collegiate Institute is a secondary school in Toronto, Ontario, Canada. It is located in the L'Amoreaux neighbourhood of the former suburb of Scarborough. It is operated by the Toronto District School Board and previously by the Scarborough Board of Education. The school's motto is "Prudentia et Scientia" (Vision and knowledge).

Sir John A. Macdonald Collegiate Institute was designed by the architectural firm, Gordon S. Adamson and Associates. The school building, originally named O'Sullivan Secondary School, was constructed in 1963 and opened in the fall of 1964 when there was only farmland around it, and as the population in the area grew, so did the school. During construction, O'Sullivan was renamed to Sir John A. Macdonald Collegiate Institute, after Canada's first prime minister, John A. Macdonald, in which the colours red, black, white and purple were chosen, with the latter colour taken from the $10 Canadian banknote.

As its eleventh collegiate, the school's main building was then extended to have more classrooms, along with larger rooms used for music, art, and autoshop. MacDonald celebrated its 50th year on September 26, 2014.

Currently, as of 2025, it is unknown whether if the school district plans to change the school's name following the revelation of the school's namesake was the architect of the Canadian Indian residential school system. The changes comes after the death of George Floyd in 2020 and the discovery of 215 mass graves in a residential school in Kamloops in 2021 to address systemic racism.

• Mike Johnson, retired NHL Hockey player (with the Toronto Maple Leafs, Tampa Bay Lightning, Phoenix Coyotes, Montreal Canadiens, and St. Louis Blues)
• David Furnish, filmmaker/director/producer and husband of Elton John
• Neil Crone, actor, comedian, and motivational speaker
• Eric McCormack, actor, producer and musician, star of TV series Will and Grace
• Mike Myers, comedian and Hollywood movie actor (attended Macdonald, but graduated from Stephen Leacock C.I.)
• Duff Gibson, 2006 Winter Olympics gold medalist in singles skeleton; firefighter with Calgary International Airport

• Shaun Chen, former Toronto District School Board Trustee (Ward 21) and current Member of Parliament for Scarborough North
• Michelle MacPherson, 1984 Summer Olympics bronze medalist, 1982 Commonwealth Games double bronze medallist and gold medal relay, swimming
• Brad Park, retired NHL player (with the New York Rangers, Boston Bruins, and Detroit Red Wings), member of the Hockey Hall of Fame; briefly coach with the Red Wings
• Barbara Gowdy, novelist and short story author
• Michael Rudder, Canadian stage, film and voice actor, survived shooting in Mumbai, India
• Mike Levine, bass player for Triumph
• Sherko Haji Rasouli, football player for the BC Lions
• Rod Connop, CFL All-Star and Canadian Football Hall of Fame inductee
• John Anderson, retired NHL hockey player (with the Toronto Maple Leafs, Quebec Nordiques, Hartford Whalers)

• Education in Ontario
• List of secondary schools in Ontario

• "Sir John A Macdonald Collegiate Institute". Archived from the original on 2014-09-05. Retrieved 2024-12-27.
• "Toronto District School Board > Find your... > Schools". Archived from the original on 2013-10-22. Retrieved 2024-12-27.