Douglas, 58, who is serving his fourth two-year term, told a news conference at Montpelier he will not seek another political office, The Washington Post reported.
"It's been the great privilege of my life to serve the people of this state that I love so well," Douglas said. "But as any farmer knows after many years of working sunup to sundown, seven days a week, there comes a time to turn over the reins to fresh arms. For me, that time is approaching."
Lt. Gov. Brian Dubie is a Republican, but it's unclear whether he wants to run for the state's top job.
"The governor's announcement today changes the political landscape in Vermont. As Vermonters reflect on this new landscape, I will contemplate my options. Right now, I will focus on doing my job," Lt. Gov. Brian Dubie said.
Dubie was noncommittal regarding his role in the 2010 gubernatorial race, the newspaper said.