Jesse L. Martin on Starring in NBC’s Series ‘The Irrational’

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 F.B.I. 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.