Toronto Mayor David Miller announces that he will not seek re-election. (CBC)

Mayor David Miller shocked Torontonians on Friday, announcing he will not be seeking re-election.

"I'm announcing this morning that I will not be seeking a third term as mayor of Toronto in next year's municipal election," he said.

"While it has been a difficult decision, I feel secure in my priorities, proud of my record, and confident in my vision of the city I love."

Miller told a mid-morning news conference outside the mayor's office at City Hall that he made the decision years ago, because "the pressures on me as a father and a husband have been immense."

Miller said he recently reconsidered because of constant media speculation asking if he was going to run again. "Of course I could only answer, 'Yes,'" he said.

The Toronto mayor also said that after an "enthusiastic" meeting with his campaign team he had a meeting with his family and "decided I had to make this announcement today."

Miller refused to take any questions from reporters or explain why he had done such a dramatic political about-face.

On Aug. 4, only days after ending a 39-day strike by civic workers Miller told a news conference he was "proud of the track record I have as mayor" and was looking forward to a third election campaign.

Miller was first elected in 2003 and then re-elected in 2006. He said in the past that he wanted to serve three terms in the mayor's office — claiming that was the length of time needed to effect real change in city government.

But on Friday he declared he had done everything he promised, so he could leave with a clear conscience.

"My reasoning is simple," said Miller. "I've accomplished what I set out to do."

There are no official challengers for Miller's job, but there are hints that former provincial Progressive Conservative leader John Tory may make a second run for office. He was defeated by Miller in 2003.

The other rumoured candidate is provincial deputy premier George Smitherman, who raised his profile during the civic workers strike by organizing street cleaning squads.