Coleman made the announcement this afternoon at his office in St. Paul. He's up for re-election to a second term as mayor next month.
Coleman, a DFLer, had been looking at the wide-open 2010 governor's race, and Republicans had been accusing him of running for both offices at the same time.
Coleman said he made up his mind this morning that he would not run.
"My work is here. I was elected four years ago to move St. Paul forward, but my work's not finished," said Coleman. "And there was no way that I could ask the voters for their confidence and their support for another four years, knowing that I was going to spend 100 percent of my time for the next seven months, at least, running for governor. There are too many critical issues facing the city of St. Paul right now."
Coleman said the Central Corridor light rail line is a key concern.
"Even though we actually have begun construction on the critical phase of Central Corridor, we are not fully funded yet. And I want to make sure that receives my full attention," said Coleman. "I couldn't do that if I was engaged in 14 different debates every week across the state of Minnesota."
Coleman said his decision surprised him as much as anyone else -- and many political observers were surprised, since Coleman had openly expressed an interest in running for governor in recent weeks.
Speaking at the Minnesota State Fair several weeks ago, Coleman said, "I have not made a secret of the fact that I'm interested in looking at the governor's race, and talking to folks about what they're looking for in the next leader of the state of Minnesota."
Coleman hired a high-powered team in August for his mayoral re-election effort, fueling speculation that the mayor had higher political ambitions.
Mandy Grunwald, who worked for the campaigns of Bill Clinton, Al Franken, Amy Klobuchar and Paul Wellstone, had joined the team as a media consultant.
Minneapolis Mayor R.T. Rybak has also strongly hinted at entering the governor's race. The two-time mayor is also running for re-election, and has said he will not formally announce his intentions until after the November election.
Rybak would face a crowded field of DFL candidates, including: House Speaker Margaret Anderson Kelliher, Ramsey County Attorney Susan Gaertner, state Sens. Tom Bakk and John Marty; state Reps. Tom Rukavina and Paul Thissen, former U.S. Sen. Mark Dayton, and former state legislators Matt Entenza and Steve Kelley.
Republican candidates include: state Sens. Mike Jungbauer and David Hann; state Reps. Marty Seifert, Paul Kohls, Tom Emmer; environmental activist Leslie Davis, former lawmaker Bill Haas, former state auditor Pat Anderson, and businessman Phil Herwig.