Federal politics (2008–2011)

Crombie was elected as the MP for Mississauga—Streetsville in the 2008 Canadian federal election, defeating incumbent MP Wajid Khan, who had previously crossed the floor from the Liberals to join the Conservative Party.

Following her election, she served as co-chair of the Liberal Caucus Outreach Committee alongside Justin Trudeau^[5] and took on the role of the Liberal Party critic for Crown corporations under leader Michael Ignatieff.^[6]

In the 2011 federal election, Crombie was defeated by Conservative candidate Brad Butt; Butt received 43.8 percent of the vote to Crombie's 36.9.^[7]

Municipal politics (2011–2024)

On September 19, 2011, Crombie secured a seat on Mississauga City Council through a by-election, succeeding Eve Adams as Councillor for Ward 5. She won by a margin of slightly over 200 votes, defeating Carolyn Parrish and Eve Adams's ex-husband, Peter. On December 12, 2012, Crombie faced charges related to alleged violations of election finance rules from her councillor run, but these charges were later withdrawn in February 2013 after the Crown determined that financials needed formal auditing before any charges could be considered.

After Hazel McCallion, the long-serving mayor of Mississauga, retired, the 2014 mayoral election became the city's first genuinely competitive race in years. Crombie, along with former city councillor Steve Mahoney and others, declared their candidacies. Despite Mahoney leading in polls for much of 2014, McCallion's endorsement of Crombie on October 12 shifted the dynamics, giving Crombie a 25-point lead over Mahoney. In the election, Crombie secured victory with 63.49 per cent of the vote.

Crombie announced her bid for re-election as mayor on October 27, 2017, and emerged victorious in the 2018 mayoral election with over 75 per cent of the vote. She secured her third term in the 2022 mayoral election by another wide margin.

Throughout her mayoral tenure, Crombie advocated for the dissolution of the Region of Peel, the upper-tier municipality which Mississauga is part of.^[8] In 2023, the provincial government of Doug Ford supported the split.

During a Liberal leadership debate on The Agenda with Steve Paikin, hosted by TVO on November 15, 2023, Crombie declared that she will not seek re-election in 2026, concluding her tenure as the mayor of Mississauga after three terms. She later stated that she is likely to run for MPP in the 2026 provincial election.^[9]

After winning the 2023 leadership election of the Ontario Liberal Party, Crombie announced on December 13 that she would resign as Mississauga mayor, effective January 12, 2024, after completing the city's and Peel Region's budgets before stepping down.^[10][11]

Provincial politics (2023–present)

In early 2023, media reports, citing sources within the party, speculated that Crombie was contemplating a run in the 2023 Ontario Liberal Party leadership election scheduled for December. Her active participation was noted during the Ontario Liberal Party's annual general meeting in March 2023 and the Liberal Party of Canada's national convention from May 4-6 in Ottawa.

On May 23, 2023, Crombie confirmed the speculation by announcing the formation of an exploratory committee. She indicated that her final decision would be disclosed in the coming weeks. Subsequently, on June 14, she officially launched her campaign at an event in Mississauga. She took an unpaid leave of absence from her role as mayor of Mississauga starting October 7. However, she returned on November 27 to participate in the city's budget process. Crombie was considered the frontrunner in the Liberal leadership race.^[12][13] She was elected party leader at the December 2, 2023, on the third ballot.^[14]

Provincial

Municipal

Federal