NDP Leader Tom Mulcair's resolve to oppose the Trans-Pacific Partnership was born out of his father's sudden job loss and the cascading effect it had on him and his family when he was 18 years old.

Mulcair believes the trade deal threatens jobs in the manufacturing and dairy sectors.

"When I meet families on this tour, who have lost their jobs, or are under threat of losing their jobs, I do not think of statistics, I look those people in the eye and I know what they are going through, because I have," Mulcair told CBC News in an exclusive interview Thursday.

His father, Harry Donnelly Mulcair, had 10 children at the time he was laid off, with eight still at home.

The family was forced to sell its house in Chomedy, north of Montreal, and move into a cottage in the Laurentians, while Mulcair's mother, Jeanne, returned to work.

Mulcair said those tough times in a modest cottage were a struggle for his parents — and especially his dad — a memory Mulcair says he still carries with him today.

"It was very tough on him, he was a very proud dad and breadwinner," Mulcair said.

"I saw what it was like for the head of a family at the time, it was almost always the dad, to lose the livelihood of the family and to struggle, because like most families, especially with a large number of kids, there was no extra money."

Roofing work

The layoff also had an effect on Mulcair, even though he was not living at home, when he had to find a way to pay for school without the support of his parents.

Because his father had previously been employed, Mulcair was also ineligible for student loans.

"I really had to decide whether I was going to stick this out. I had worked in construction during the summer, tarring roofs in Montreal, and I had some money, but not enough to get by."

Mulcair managed to make it work, borrowing cash for books from his elder sister, Colleen.

The repercussions of that time on his family, though, were significant, and Mulcair said it led him to believe government cannot be the preserve of the wealthy and privileged.

"You can lift yourself up from that, but I think we also need people in government who understand, from having lived it, what it is to be middle class, and frankly, at that stage well below middle class."

That comment could be taken as a slight against Liberal Leader Justin Trudeau, who is the son of a former prime minister.

But by the time Mulcair was a minister in the Quebec Liberal government of Jean Charest, his approach to politics had shifted.

Straying off-course

It was a drift that was corrected sharply in 2004 when Mulcair's political mentor Claude Ryan was on his deathbed. Ryan is an important figure in Quebec politics who clashed both with separatists and the federalist politician Pierre Trudeau.

Mulcair said Ryan was a dyed-in-the-wool social democrat, who, as he was coming to the end of his life, gently rebuked Mulcair for drifting from the political values he learned as a young man.

"[Ryan] was not very happy with what the Charest government had been doing on the social side of things, and he told me so in so many words, and he said, 'Never forget the only reason we go into politics is to be able to help people,'" Mulcair recalled Thursday in an interview in Alma, Que.

"And that was a bit of a slap in the face, but in the nicest Claude Ryan type of way, which was, 'Don't forget why you are here.'"

Mulcair left provincial politics in 2007, and after exploring options with all federal parties, settled on running for the NDP.

He has been accused of dragging the party toward the middle and away from its left-wing, activist roots.

But Mulcair maintains he has strong social democrat credentials, forged through the experience of his early life.

"I think what it has given me is a sense of what families go through when we talk about lost jobs, and the types of jobs being created today, which are not enough for a family to live on," Mulcair said.

"For me this hits right home. I have lived it, and I think of it, and I want people to have a job that a family can live on. That's what I want to get us back to in Canada, not these precarious low-paid part-time jobs that we've got now."