NEW YORK, NY.- Jesse L. Martin can tell when you’re lying. You might look away, he said. You might look down. Your nose will perspire and you will feel compelled to touch it. “There’s also intense eye contact,” he said, demonstrating this across a low table in the bar of a downtown hotel last week.

Martin, an actor who spent his young adulthood in New York but has since relocated to Vancouver, British Columbia, was in town for a few days to promote “The Irrational,” the NBC procedural in which he stars. (The final episodes of its first season are now airing; the network has already renewed it for a second.) Martin, 55, plays Alec Mercer, a professor of behavioral science at a fictional university. Somehow, Alec spends more time assisting the FBI than he does in the classroom. (That’s tenure for you.) He solves each week’s case by applying one or more behavioral science concepts — the halo effect, the Barnum effect, paradoxical persuasion.

Almost pathologically observant, Alec is based on Dan Ariely, a superstar in the field of behavioral science, and Martin has absorbed a morsel of those powers. Looking around the room over the top of a club sandwich, he could tell at a glance who was an artist, who was wealthy (“It has everything to do with all the ways they don’t show it,” he said.). The chicken, he observed, was “kind of dry.”

That day, he was dressed elegantly, if playfully, in jeans, a white shirt, a black blazer, a burgundy pocket square and the knit golfing cap he often favors. (Martin has always been a hat guy.) His other accessories: an easy smile and a gleam in his eye that softens many of his characters. Acting is arguably lying for a living. Martin — a member of the original Broadway company of “Rent” who then spent nine seasons on NBC’s “Law & Order” and eight on The CW series “The Flash” — does it cleanly, candidly, without tells.

“The spirit’s different,” he said of the kind of fabrication that acting requires. “It’s joy for me, so it would never feel like a lie.” If he lied during our conversation — about the work, about the chicken — I couldn’t detect it. “The Irrational” is inspired by and named for Ariely’s book “Predictably Irrational: The Hidden Forces That Shape Our Decisions.” A classically trained actor, Martin has always dreamed of going from one stage role to the next. “Every time I think about doing any play, a whole different part of me gets jazzed,” he said. But he also describes himself as highly rational, and so has instead spent most of his career on television procedurals.

“I’ve always been practical to a fault,” he said, not without some regret.

It was practical to take the job on “Law & Order” as Detective Ed Green, and it was practical to stay so long. The show was filmed in New York City, then his home. And although Green was, as Martin described him, a “just-the-facts” character, the role allowed Martin to act opposite some of New York’s finest performers. He took a brief hiatus to do the “Rent” movie (2005) and finally left the show in 2008 to pursue more stage work. He acted opposite Al Pacino at Shakespeare in the Park and then on Broadway when “The Merchant of Venice” transferred in 2010.

After a stint on “Smash,” an NBC musical-drama, Martin accepted a role on “The Flash,” noting that the part, a detective who is also a father figure to the central superhero, offered greater emotional heft. Besides, he was by then, he said, “a product of television,” accustomed to its rhythms and its rewards. After eight seasons and a back injury, he left that, too, appearing only sporadically in the ninth season.

Martin’s arc had run its course and he wanted to go back to the theater, “back to the circus,” he said. But almost immediately, NBC approached with “The Irrational.” The premise intrigued him, as did the chance to finally play a lead rather than a sidekick.

“This one, it’s used all of me,” he said. “I get to use every skill I have to play Alec.”

Alec has more empathy than most of Martin’s characters and greater emotional intelligence. He also has more of a backstory. The show provides him with an FBI agent ex-wife, a computer-whiz sister and ample burn scars, remnants of an unsolved bombing. Alec is self-conscious about his scarring, but if the show wanted to make Martin appear unhandsome, which he pushed for, it should have tried harder. “They needed to make it palatable,” Martin said of the prosthetics.

Playing Alec has yet to give Martin a thorough understanding of behavioral science, but it has made him uncomfortably aware of human behavior. “I feel weird walking around, watching my friends’ behavior, my family’s behavior,” he said. “But I can’t help it.”

Still, he compares his powers, which I had goaded him into demonstrating at the hotel bar, unfavorably with those of Alec, or Ariely. “When you’re with him, you’re quite sure that you’re part of an experiment he’s just not telling you about,” Martin said of Ariely. “The more you try to mask, the more you give away.”

Ariely and some of his colleagues have recently come under scrutiny after allegations of data manipulation, but “The Irrational” and Martin profess an absolute belief in the science. That’s good, because it would be difficult to justify the week-in, week-out demands of a procedural otherwise.

“It’s relentless, absolutely relentless,” Martin said of the show’s pace. “But I absolutely love the work.”

He might, he suggested, even love it too much, a devotion that borders on the irrational, the impractical. Martin has never been especially open about his personal life, perhaps, he admitted, because there has rarely been much of a personal life to speak of.

“I just don’t think it’s that interesting,” he said. “It’s not as interesting as the work I do.” That work, he said, had ruined several relationships. He ran a brief thought experiment, wondering what his life might be like if he cared less about his work. He probably would have more of a life outside of his career, Martin decided. He probably wouldn’t be so private about it.

“There’s a world I’m missing,” he said. “And believe me, it stings a lot more these days than it used to. I say to myself, ‘This just can’t be everything. This can take up a lot of time, this job. But it can’t be everything, right?’” A few years ago he got a dog, Romeo, which has given him just a little more life beyond work. (It also explains why a city person like Martin now lives in the Vancouver suburbs.)

But for now, the work remains. He’s too dedicated to it to change his behavior. And the salary doesn’t hurt. “I always joke, ‘Romeo needs steaks,’” he said. “Only the best for my puppy.”

This article originally appeared in The New York Times.