Foreign Affairs Minister John Baird says he didn't want to become one of the "lifers" in federal politics, which is why he made the stunning decision to leave politics to pursue career opportunities in the private sector.

"There is, I guess, a notion, where people become lifers. I've always thought it's good to come in, make a contribution and move on to something else. I did that 10 years ago at Queen's Park and I'm doing the same now," Baird told CBC's chief correspondent, Peter Mansbridge, in a sit-down interview Wednesday, the day after announcing his resignation in Parliament.

Baird's exit caught everyone — from the prime minister to his political colleagues — completely off-guard

"I just decided after 20 years in the arena it was a good time for me to do something else," the Conservative MP, who represents the riding of Ottawa West-Nepean, said in the interview, which airs Saturday on Mansbridge One on One..

"Going out on top was always an objective of mine in politics, and I'm very pleased with what our government has been able to accomplish, and it was a good time for me personally."

The sudden death last year of long-time friend and colleague Jim Flaherty, who died of a heart attack a month after stepping down as Canada’s long-time finance minister, was another key factor.

Baird told Mansbridge he was shaken by the death of Flaherty, with whom he had served in cabinet in both Ontario and Ottawa.

"That really shook me up and it was a reminder that, if you want to do other things and opportunities present themselves, you should reflect on that."

Fiercely partisan

The 45-year-old Baird developed a reputation over the years as being fiercely partisan, quick to take on opponents, and unwavering in his loyalty to both party and leader.

But it was a more reflective Baird who sat down with Mansbridge.

For starters, he emphatically denied the partisan tag.

"I take on a partisan role when I have to. You know, if someone gets up in question period and smacks you over the head with a 2x4, I'm not a piñata. I give as good as I get. But I think I always have been able to work with MPs across the aisle."

Denies rift with PM

Baird said he was relieved to be leaving, but denied rumours of a rift with Prime Minister Stephen Harper or that his influence inside cabinet had waned.

"We debate, every year, hundreds if not thousand of issues," Baird said when asked about his relationship with the PM. "But I can tell you, certainly in my time as foreign minister, we have been so closely aligned, whether it is Russian aggression in Ukraine, whether it's on issues in the Middle East, Israel or the war on ISIS, we have a remarkably similar world view."

Baird served 10 years in the Ontario government of Mike Harris and another nine years in Harper's cabinet. He was tapped to deliver some of the Conservatives' key priorities, including the Federal Accountability Act in 2006 that limits the jobs politicians can take after leaving office.

He sidestepped questions about where he'll wind up, saying, "I have nothing to announce right now."

Tories lose profile in Ontario

Baird’s departure is a significant blow for the Conservatives, coming just months before the party tries for a fourth consecutive mandate.

Foreign Minister John Baird tells the CBC's Peter Mansbridge he was determined to go 'out on top.' But his departure leaves Prime Minister Stephen Harper with a weakened bench in Ontario. (Amr Nabil/Associated Press) Baird, and Flaherty, were key architects of the party's campaign in Ontario. The province — with its 121 seats in 2015 — will be a key battleground again, but the Conservative Party will go into the election missing its two most senior and politically effective politicians from the province.

Harper had asked all of his cabinet ministers last summer if they intended to run again. Those who said they wouldn't were replaced as the prime minister built a cabinet to take the Conservatives into the next election.

So Baird's decision was both a surprise and a setback.

Harper must now find a replacement who can step seamlessly into the challenging foreign affairs role at a time when Canada is coping with several difficult issues, most notably a deadline next month to decide whether to extend the current mission in Iraq, and what role Canadian Forces members should play in the battle against ISIS.

Ed Fast to fill in

Trade Minister Ed Fast will fill the role on an interim basis, and insiders say Harper isn't likely to name a permanent successor until next week, after his office, once again, has asked cabinet ministers whether they are in or out for the coming election.

As for Baird, he's certainly at his most marketable after four years as foreign affairs minister. It's given him a unique, front-row seat to global events, and contacts around the world that few people in Canada can match. It's a desirable mix for companies with business interests overseas to have someone who can pick up the phone and make things happen.

Mansbridge One on One airs on CBC News Network Saturdays at 6:30 p.m. ET and on CBC-TV Sundays at 1 p.m.