Jim Rondeau said Monday he no longer has the same energy or enthusiasm for the job and will not seek re-election next year.
Rondeau said Premier Greg Selinger's decision to drop him from cabinet in October 2013 is one reason he's leaving, but not the main one.
"The majority of my decision — the vast majority — was whether a) you have five more years of spending 40, 50, 60 hours a week and b) you have the energy to do what I believe you need to do as a constituent (member of the legislative assembly)," Rondeau said in an interview with The Canadian Press.
Rondeau, 56, was first elected to the legislature in 1999 in the Assiniboia constituency in west Winnipeg and served a decade in cabinet starting in 2003. As minister of healthy living, he ushered in the province's ban on smoking in public places as well as a law requiring children to wear helmets while riding bicycles.
He also served for a few years as minister of industry, economic development and mines.
Rondeau was one of three cabinet ministers who were demoted in a 2013 shuffle. He said Monday he was not given a reason for the move.
"I don't know why I was demoted. Actually, now I'm very much at peace with where I am. I get time to myself. You're no longer managing hundreds of millions of dollars of budget."
When a caucus revolt erupted last fall and Selinger called for a party leadership race, Rondeau backed Steve Ashton, who finished last in the three-candidate contest.
Rondeau's decision to leave politics seems to have been a sudden one. In a letter to his constituency association on the weekend, he said he had been planning to run for re-election in the province-wide vote slated for next April.
"I had submitted my application to seek the nomination as a candidate in the next provincial election to (NDP) provincial office around Christmas, and again dropped it off a few months ago, and have not heard anything," he wrote.
"So I will be forwarding them a note as to my decision to not continue to seek the nomination."
Rondeau said he made his decision so that the NDP can find another candidate in plenty of time for the election.
He had been touted by some pundits as a possible federal politician, but said he wants to leave politics behind and spend more time with his husband.
"We said, 'Hey, is this where you want to go out — when you have a good reputation and ... you've done all the work?' And the answer is yes. I've had a great run."
Selinger issued a brief written statement Monday that thanked Rondeau "for his extraordinary energy and hard work for the residents of Assiniboia, our government and party, and ... for a truly outstanding career."