A by-election was held on October 24, 2016,[1] in the riding of Medicine Hat—Cardston—Warner, which had been vacant since March 23, 2016, when Conservative Party of Canada MP Jim Hillyer died in his office following a heart attack.

Retired Medicine Hat Police inspector Glen Motz[1] defeated businessman Brian Benoit, former Cardston-Taber-Warner and Calgary-Glenmore MLA Paul Hinman, lawyer Michael W. Jones, and party worker Joseph Schow for the Conservative nomination, which was held in late June.

A by-election was held on April 3, 2017,[2] in the riding of Ottawa—Vanier, which had been vacant since the death of Mauril Bélanger on August 16, 2016, from amyotrophic lateral sclerosis (also known as Lou Gehrig's disease).

After several prominent potential candidates, including Bélanger's widow Catherine Bélanger, Ottawa councillors Tobi Nussbaum and Tim Tierney, and 2014 council candidate Catherine Fortin LeFaivre[48][49] declined to run, eight candidates sought the Liberal nomination: Senate staffer Khatera Akbari, lawyer Jean Claude Dubuisson, communications consultant Mona Fortier, Liberal staffer Eric Khaiat, former Cape Breton Highlands—Canso MP Francis LeBlanc, public servant Ainsley Malhotra, former executive director of The Humanitarian Coalition Nicolas Moyer, and Unique FM executive director Véronique Soucy.

[50][51] Unsuccessful 2015 candidate Emilie Taman, a University of Ottawa law professor and daughter of former Supreme Court Justice Louise Arbour, ran again for the NDP.

[48] Parliament Hill staffer Adrian Papara defeated former New Brunswick MLA Joel Bernard for the Conservative Party nomination, decided on February 16.

[53] The riding of Calgary Heritage became vacant when former Prime Minister of Canada Stephen Harper resigned his seat on August 26, 2016, to return to private life, including accepting directorships on corporate boards and establishing a consultancy firm.

[3] The electoral district was created for the 2015 federal election and has had Harper as its only MP; however, it is largely composed of the former riding of Calgary Southwest which was held by conservative parties throughout its existence.

Former diplomat Stephanie Kusie[65] defeated entrepreneur Myles McDougall[66] and local federal riding association president Jack Redekop[67] for the Conservative nomination, held on January 14, 2017.

[63] The riding of Markham—Thornhill was vacated on February 1, 2017,[8][9] following the appointment of Liberal MP and Minister of Immigration, Refugees and Citizenship John McCallum as Ambassador to China.

Justin Trudeau's director of appointments and former senior Queen's Park staffer Mary Ng,[71] defeated small business owner Nadeem Quereshi[66] and technology entrepreneur Afraj Gill[66] for the Liberal nomination on March 4, 2017.

[75][76] Radio host and newspaper columnist Gavan Paranchothy defeated CIBC economist Theodore Antony,[66] former senior Queen's Park staffer Lara Coombs,[66] former Don Valley East MP Joe Daniel,[66] and parental rights advocate John Himanen[66] for the Conservative Party nomination on March 8.

[80] The riding of Saint-Laurent was vacated on February 6, 2017,[8][10] following the appointment of Liberal MP and former Minister of Foreign Affairs Stéphane Dion as Canada's Ambassador to the European Union and Germany.

[86] The riding of Sturgeon River—Parkland was vacated on July 4, 2017, due to the resignation of Rona Ambrose whose term as interim Conservative Party of Canada leader ended with the election of her successor on May 27, 2017.

[110][111] Ward 39 (Scarborough Agincourt – North) city councillor and former Scarborough—Agincourt MP Jim Karygiannis declined to run for the nomination, but threw his support to Yip.

York Region District School Board Trustee Allan Tam as well as former teacher and immigration officer Sarah Chung[114] were both rejected by the party.

[115] Scarborough-born federal NDP leader and former GTA MPP Jagmeet Singh, who does not have a seat in the House of Commons, ruled out standing as a candidate in the by-election.

[16] Centreville-Wareham-Trinity Mayor and former president of the Federation of Municipalities in Newfoundland and Labrador Churence Rogers[119] defeated[120] comedian Pete Soucy,[121][122] provincial and federal Liberal party organizer Larry Guinchard,[123] RCMP officer Dale Foote,[124] and North Harbour farmer, former search and rescue coordinator, and 2008 Conservative Party candidate in St. John's South—Mount Pearl Merv Wiseman[125][126] for the Liberal nomination.

[17] Former federal cabinet minister and Delta—Richmond East MP Kerry-Lynne Findlay[133] defeated[112] Fraser Institute policy analyst and former BC Liberal staffer David Hunt[134] and police officer Bryan Tepper for the Conservative Party nomination.

Ritz had been Battlefords—Lloydminster's only Member of Parliament, holding the riding since its creation for the 1997 election, first as a Reform Party of Canada MP, then on behalf of the Canadian Alliance and since 2003 as a Conservative.

Former parliamentary staffer Rosemarie Falk defeated[138] Langham Mayor John Hildebrand, small business owner Aron Klassen, Kindersley CAO Bernie Morton, and farmer Richard Nelson to win the Conservative nomination.

[139] Meadow Lake MLA and former Desnethé—Missinippi—Churchill River MP Jeremy Harrison was rumoured to be a candidate for the Conservative nomination,[140] but did not make his intentions known before the cut-off date to join the race.

Port Saguenay board member Lina Boivin, who was endorsed by Lemieux,[145][146] defeated former Saint-Charles de Bourget mayor Michel Ringuette[147] for the Liberal nomination,[148][149] held in May 2018.

[150][151][152] "Promotion Saguenay" Director of Industrial Development and Corporate Affairs Claude Bouchard had his candidacy rejected by the federal Liberal party.

[153] Dany Morin and former Ontario MPP and federal NDP leader Jagmeet Singh both expressed interest in running for the nomination but decided against it.

Former Chicoutimi—Le Fjord BQ MP Robert Bouchard, Saguenay firefighter Mario Gagnon,[159] and UQAC political science professor Michel Roche declined to run for the nomination.

[21] The seat for the electoral district of Leeds—Grenville—Thousand Islands and Rideau Lakes has been vacant since May 2, 2018 when Conservative MP Gord Brown died of a heart attack in his Parliament Hill office in Ottawa.

[163] In addition, Edwardsburgh/Cardinal town councillor and federal riding association president Michael Barrett,[164] government-relations specialist Stephanie Mitton,[164] and Anne Johnston,[165] a former aide to Leeds—Grenville—Thousand Islands and Rideau Lakes MPP Steve Clark also ran for the Conservative nomination.

Former Canadian Senator and interim Leader of the Opposition in the Ontario Legislature Bob Runciman was rumoured to be interested in seeking the Conservative nomination[166] for the by-election but decided against it after his wife encountered some health issues.

[172] 2015 Liberal candidate Adam Pankratz, a commercial banker with a local credit union, stated that he was undecided, but ultimately decided against running again.