Four federal byelections — two in Alberta, two in Ontario — will be held June 30.
Trinity-Spadina became vacant when New Democrat Olivia Chow resigned to run for mayor of Toronto.
Coun. Adam Vaughan will be the Liberal candidate for the riding after winning the nomination on May 3.
Vaughan will give up his seat on Toronto City Council when the writ drops for the byelection on Tuesday.
“It has been an incredible privilege to serve the people of Ward 20 for two terms, but it’s time Toronto had someone in Ottawa who works with us, instead of ignoring the problems that are unique to Canada’s biggest cities,” said Vaughan in a statement.
“I believe the best person to bring about that change is Justin Trudeau and I want to join him in Ottawa to put a national spotlight on issues like affordable housing and gridlock.”
Activist and former senior advisor to the Stephen Lewis Foundation Joe Cressy will run for the NDP in Trinity-Spadina. Cressy’s parents were Toronto city councillors.
And in Scarborough-Agincourt, Liberal stalwart Jim Karygiannis stepped down to run for a seat on Toronto city council in a ward that overlaps much of the federal riding.
Liberal Arnold Chan and Conservative Trevor Ellis are on the ballot in that riding.
The Alberta constituency of Fort McMurray-Athabasca was vacated by Conservative MP Brian Jean, who stepped down in January, citing a desire to spend more time with his family.
Conservative MP Ted Menzies resigned his southern Alberta seat in the riding of Macleod in November to become president and chief executive officer of CropLife Canada, a trade association for plant-life technologies.
However, Prime Minister Stephen Harper did not call a byelection for the Ontario riding of Whitby-Oshawa, left without an MP upon the recent death of Conservative Jim Flaherty, the former finance minister.
The byelection announcements come amid a flurry of behind-the-scenes preparation and nomination meetings for a general election next year.
With files from Toronto Staff