Montreal mayor Gerald Tremblay has resigned after witnesses linked him to illegal party financing skimmed from city construction contracts as part of an alleged mafia scheme.
Tremblay, 70, has led Canada's second-largest city since 2001 and would not have faced re-election until the end of his latest mandate in 2013.
"After 25 years of public service, I am leaving public life," he said in a televised address on Monday .
A commission headed by Superior Court Justice France Charbonneau had heard in recent weeks that the mayor's political party received kickbacks from construction bids.
Witnesses told the commission investigating alleged graft, bid-rigging and kickbacks in the awarding of government contracts that the mayor was aware of illegal party financing and campaign spending.
Tremblay flatly rejected the accusations.
"Long ago, my father told me never to go into politics, because it's dirty and I would be destroyed," he said. "But my passion and love for Quebec and for Montreal plotted the course I should take. I devoted all of my energy and I gave my best."
Tremblay expressed regret that his trust had been betrayed, and said he accepted "full responsibility" for the consequences.
The Charbonneau commission was launched after a leaked police report pointed to evidence that construction companies were banding together to keep prices high - and possibly had links to organised crime. It will release its findings next year.
Montreal is known for its long-time links to organised crime, something underscored late Sunday when a man in his 70s was shot dead in front of his home. Police said Joseph "Joe" Di Maulo was widely believed to have been the second-in-command of the city's mafia.