NEW YORK – For much of last season on Showtime’s “The Big C,” Oliver Platt played a husband with no clue his wife had been diagnosed with life-threatening cancer.

It was hard playing those scenes “in the dark,” he says. “You had to really focus and forget that you knew.” But how? “Well, you just do it. It’s your job. You pretend.”

Platt is pretty good at that.

But as his dark though ultimately life-affirming comedy airs its second season Mondays, Paul is fully informed about the grave condition of his mate, Cathy (played by series star Laura Linney).

For nearly a quarter-century, the 51-year-old Platt has flourished as a character actor who brings a lovable roguery, and insight as well, to his roles. Moon-faced and bulky at 6 feet, 3 inches, his performances include the shrewd White House counsel challenging President Bartlet on “The West Wing” and Yankees owner George Steinbrenner in the miniseries “The Bronx Is Burning.” Currently, he’s a CIA team leader in “X-Men: First Class.”

Platt cites his distinctly non-leading-man looks as an asset.

“What I was told early on was that, as an actor, I had a uniqueness: There wasn’t anybody who looked like me, for better or worse, and we don’t need to get into that any further, thank you,” he says, chuckling.

The son of a career diplomat, he grew up in Washington and throughout the Far East as the family was frequently re-stationed.

“I was always a new kid in school, and I figured out (acting) was a way to plug in: I’d try out for a play and then I would have a group of friends,” he says. But it was more than a coping device. “I also loved doing it.”

Bitten by the bug, he majored in drama at Boston’s Tufts University, then spent several years in the local theater scene before embarking for the big time in New York. He landed his feature film debut in the 1988 hit comedy “Married to the Mob.”

The career he has enjoyed since then has been busy and eclectic.

Platt married in 1992, and he and wife Camilla have three kids ages 16, 14 and 12.

“I don’t take it for granted that I’ll be offered work,” he says. “There’s a sense of gratitude that I’m able to support my family doing this.”

They live in Greenwich Village, near the breakfast spot where Platt has joined a reporter one recent morning. Chained outside is his bike, which is a no-frills affair, oversized with a 70-cm frame and sporting a plastic dairy-crate basket lashed to the front wheel. After the interview, Platt will pedal off to do chores.

Through the years, he’s been able to balance his personal life and career, never venturing too far from home for too long (“The Big C” is shot within commuting distance in Connecticut).

“Family life to me is incredibly important and fulfilling, and it keeps the noise of show biz in perspective for me,” he says, adding, “My wife is very grounded, unimpressed by the superficial trappings of show biz.

“When I was younger, I had to do a bit of disentangling myself from the acting world. When I got on stage, it became a little too important for me. I needed to turn acting back into a job, instead of a survival mechanism.”