Governor General David Johnston, acting on the advice of Prime Minister Stephen Harper, issued the writ of election for the by-election on February 6.

[5] The riding of Calgary Centre was vacated on May 30, 2012, when Conservative MP Lee Richardson resigned to accept a position as principal secretary to Alberta Premier Alison Redford.

[21] Bowmanville resident Grant Humes, the Liberal candidate in the last election, ran again,[22] while the NDP nominated Larry O'Connor, a former member of the Legislative Assembly of Ontario and former mayor of Brock.

Savoie, who held the position of Deputy Speaker of the House of Commons at the time of her announcement, cited health reasons as the key cause of her resignation.

[28] In 2011, Conservative Peter Penashue defeated sitting Liberal MP Todd Russell by 79 votes, making Labrador one of the closest races in that election.

[30] On March 14, 2013, Penashue, by then the Minister of Intergovernmental Affairs and President of the Queen's Privy Council for Canada, resigned from cabinet and from his seat with the intention to run again in a by-election.

Penashue blamed the error on a campaign volunteer, paid back the money, and announced his intention to run for re-election in a press release.

[41] Minister of Public Safety Vic Toews resigned from cabinet and as an MP effective July 9, 2013, to spend more time with his family and join the private sector.

[35][41] Former parliamentary page Natalie Courcelles Beaudry, who also works in the constituency office of Dawson Trail MLA Ron Lemieux, was the only declared candidate for the NDP nomination, which was decided on October 20.

[47] On June 19, 2013, former interim Liberal Party leader Bob Rae announced he would resign his Toronto Centre seat to become a First Nations negotiator in Ontario.

[32] Journalist, author and pundit Chrystia Freeland was nominated as the Liberal candidate defeating Todd Ross, a former senior adviser to former Ontario health minister George Smitherman and Diana Burke, former chief information security officer at Royal Bank Financial Group.

[3][50] On July 29, former MPP for the provincial electoral district of the same name and 2010 mayoral candidate George Smitherman announced he will not seek the Liberal nomination.

[51] Columnist and author Linda McQuaig,[52] is the New Democratic Party's candidate having defeated former CBC producer and MuchMusic host Jennifer Hollett,[53] and transgender rights and social housing activist Susan Gapka for the nomination.

[62] Candidates for the Green nomination were CFIA food inspector Layne Tepleski, greenhouse owner David Neufeld, and retiree Lynwood Walker.

[66] Former US Marine Frank Godon, who had previously run for the presidency of the Manitoba Métis Federation, also announced his candidacy,[35][67] but withdrew from the nomination race on September 20.

[74] Candidates for the Conservative nomination included John Barlow, who ran for the provincial PCs in Highwood during the 2012 Alberta general election, rancher and farmer Phil Rowland, former parliamentary staffer Melissa Mathieson, and businessman Scott Wagner.

[86] Other potential candidates included former Fort McMurray-Wood Buffalo MLA Guy Boutilier; former firefighter Brad Grainger; future United Conservative MLA and Conservative MP Laila Goodridge, who at the time was constituency assistant for Calgary Centre MP Joan Crockatt; and Regional Municipality of Wood Buffalo councillor Phil Meagher.

[86] Moen later made national news when he created a meme featuring himself that said "I want gay married couples to defend their marijuana plants with guns."

[93] Joe Cressy, director of the Stephen Lewis Foundation and a past campaign manager for Olivia Chow, sought the NDP nomination.

[96] Toronto city councillor Mike Layton[96] and former CBC producer and MuchMusic host Jennifer Hollett[94] were also rumoured, but announced they would not run.

On April 1, 2014, long-time Liberal Member of Parliament Jim Karygiannis announced his resignation to run in the 2014 Toronto municipal election to replace Mike Del Grande.

[105] Arnold Chan, a lawyer and former aide to Dalton McGuinty[106][107] won the Liberal nomination defeating Nikolaos Mantas, Karygiannis' former constituency assistant.

[113][114] Whitby mayor Pat Perkins defeated former electoral district association president David Glover for the Conservative Party nomination.

[115][116] Prior to her entry into the Progressive Conservative Party of Ontario leadership election, one rumoured candidate for the nomination was Christine Elliott, Flaherty's widow and the MPP for the provincial riding of the same name.

[119] Celina Caesar-Chavannes, the president of ReSolve Research Solutions Inc., a clinical trials management service she co-founded with her husband in 2004, was acclaimed as the Liberal nominee on July 17, 2014.

[118][120] On September 17, 2014, Conservative MP Rob Merrifield, first elected in 2000, resigned his seat to accept an appointment from Alberta Premier Jim Prentice as the province's envoy to the United States.

[127] On November 5, 2014, Dean Del Mastro, the independent (formerly Conservative) MP for Peterborough, resigned his seat after being found guilty on three counts of violating election spending limits.

[128][129] Prior to his resignation, the House of Commons was expected to vote in favour of an NDP proposal to suspend Del Mastro without pay, effective immediately.

On December 16, 2014 NDP MP Glenn Thibeault announced that he would be resigning from the House of Commons upon being appointed the Ontario Liberal Party's candidate in a provincial by-election.

[148] The Speaker's warrant informing Elections Canada of the vacancy was officially received on May 14, 2015 and the last day an announcement could have been made setting a by-election date is November 10, 2015.