Mayor Susan Fennell lost her bid for re-election amid a spending scandal that rocked the city northwest of Toronto.
Linda Jeffrey, a former provincial Liberal cabinet minister, defeated the incumbent and city councillor John Sanderson.
Fennell had been seeking a fifth term in office.
A recent audit found she broke municipal expense rules -- including on business-class flights, premium hotel rooms and cellphone IQ quizzes.
The expenses added up to more than $172,000, although roughly $41,000 was repaid and an arbitrator found Fennell must only pay back $3,523.
