OTTAWA – After 22 years as a member of Parliament, Scott Brison is resigning from Prime Minister Justin Trudeau's cabinet and will not be seeking re-election this fall.

Brison, who was president of the Treasury Board and MP for Kings-Hants, has informed Trudeau of his decision and said he will help with the transition for whichever Liberal—likely someone who intends to run again— that takes his ministerial role.

It is not immediately clear whether Brison intends to remain the MP for the riding up to the end of this term, or whether he’ll resign his seat in the near future.

Brison's departure has triggered a Monday cabinet shuffle to fill his ministerial vacancy, but it’s possible the prime minister will make other adjustments to his front bench at that time.

"I want to recognize the extraordinary service that Scott Brison has offered to Canadians for 22 years as a member of Parliament, as a minister in multiple governments, and as someone who has every day dedicated himself to this country, to his community, and to building a better future for all," Trudeau told reporters in Kamloops, B.C. on Thursday.

In an earlier tweet, Trudeau thanked Brison for being a "tireless champion for the people of Nova Scotia and for Canada," and called him "one of the friendliest people you will ever meet in this business."

In an interview with CTV News, Brison said "this feels very right" to him, and that he's given it his all.

"In an election year he and the government and Canadians in my view, are better served by ministers who will be candidates in the next election, with their loins girded for battle. And I did not necessarily want to be a lame duck Treasury Board President in a cabinet leading up to an election," he said. "I am walking off the field with my head held high."

Brison said he informed Trudeau around Christmas, and has no regrets about his decision.

In a video posted to social media announcing his resignation from cabinet, Brison said it was a "great honour" to represent his community, but is now ready to leave federal politics. He said he is proud of what the government has accomplished under Trudeau.

First elected in June 1997 as a Progressive Conservative, Brison "came out" for the second time in his life, this time as a Liberal when he crossed the floor to the Liberals shortly after the PC's merged with the Canadian Alliance in 2003.

Prior to his floor-crossing, Brison sought the leadership of the Progressive Conservatives in 2003. Brison served as minister of public works and government services under Liberal prime minister Paul Martin, and for some time was the party's finance critic.

Before entering public office, Brison worked as an entrepreneur and investment banker. At Dalhousie University he earned the nickname "fridge magnate," after starting an appliance-renting business as a student.

As Treasury Board president, Brison had a hand in many files across departments, and sat on several high-level cabinet committees, including as a member on the Committee on Agenda, Results and Communications, which tracks progress on the government's priorities.

This fall, Brison faced questions over his ties to Nova Scotia-based Irving Shipbuilding, in relation to suspended Vice-Admiral Mark Norman's ongoing trial for allegedly leaking cabinet secrets related to Quebec-based Davie Shipbuilding.

Norman's lawyers have accused Brison in court filings of acting inappropriately by leading an effort to end a multi-million contract with Davie for an interim naval support ship, and as The Canadian Press has reported, are planning to make him a key witness in the coming summer trial. Brison has denied any wrongdoing and has defended his involvement in the House of Commons, saying his effort to end the Davie deal was out of concern for the public purse, as the minister in charge.

Brison said that this case had "absolutely no bearing" on his decision to leave federal politics.

In Trudeau's latest cabinet shuffle in July, Brison also took on the digital government portfolio.

Now, he says he wants to spend more time with his family.

First openly gay federal minister

Brison said he and his family took stock over the holidays and made the decision together, based on three main reasons: he’s served seven terms, was ready for a change, and wants to spend more time with his family.

"They say life begins at 50, well I’m 51 and ready for new challenges," Brison said in his video message.

Brison and his husband Maxime St. Pierre are fathers to twin girls Rose and Claire, who are four years old.

He said for the early part of his life he didn't know that it would be possible for him to have children, and now that he has a young family he doesn't want to miss the important moments as they grow up.

"Some people have children easily, some people do so accidentally, neither of those options were available to Max and me, and we had to do a lot to start a family," Brison said.

On Thursday, Trudeau said that he understands the "difficult challenge" of finding time to spend with a young family with the demands of political life, and that while Brison will be missed, he respects his decision to go.

The Nova Scotian was the first openly gay federal cabinet minister, and made history again when he married his husband, something that just became legal during his lifetime.

Environment Minister Catherine McKenna applauded Brison, saying that being openly gay in political life when Brison was first appointed to cabinet "took a lot of courage."

"The House of Commons didn’t just shape my career – decisions made in that room shaped my life," Brison said in an open letter to his constituents. "Including decisions that gave me the opportunity to marry the person I love, and raise a family while being open and honest about who I am as a person."

Brison said Canada is one of the only places in the world that a life like this is possible, and thanked his community and volunteers for their support.

Colleagues, counterparts react

Brison was a key figure for the Liberals in Atlantic Canada, where the party won every seat in the 2015 federal election.

Fellow east coast MP and Liberal cabinet minister Dominic LeBlanc thanked Brison for his contribution and wished he and his family the best in their next chapter.

"It's been a privilege to be your colleague and friend for nearly two decades," LeBlanc tweeted.

"When I was first elected, Minister Brison helped champion an idea for the GOC to adopt Name Blind recruitment as a measure to build a more inclusive workforce," tweeted Immigration Minister Ahmed Hussen.

For some politicians across the aisle, this news caught them by surprise.

"What?????" Quebec Conservative MP Gerard Deltell tweeted.

"I had the honour of tangling with Scott Brison in the House many times. He is a class act. He has served the country with honour," tweeted NDP MP Charlie Angus.

Fellow Nova Scotian and former Tory MP Peter MacKay, who also left politics to spend time with his family, applauded Brison's decision.

"More family time with your young girls at home is a genuine calling," MacKay tweeted.

With files from CTV News’ Rachel Gilmore and CTV National News' Atlantic Bureau Chief Todd Battis