Linda Winer Newsday theater critic and arts columnist Linda Winer.

Winer is chief theater critic and arts columnist for Newsday, which she joined in 1987.

No star names or celebrity faces are hawking their allure from the marquee at the Helen Hayes Theatre these days. And unless you are a devoted Off-Broadway theatergoer, the name of the playwright — Stephen Karam — is not likely to scream “buy here now” at shoppers trolling Times Square.

But “The Humans,” which opens Feb. 18, comes to Broadway with some of the best reviews for any new American play in New York last year. The production arrives direct from the Roundabout Theatre Company’s Off-Broadway venue, the Laura Pels Theatre, with the same six marvelous actors — treasures to regular denizens of the nonprofit theater but hardly TV-gossip magnets. And none, not one, has been recast with a movie star to accommodate the costly and elusive Broadway marketplace.

However surprising this sounds, probably no one is as shocked as Karam, who tells me that his career trajectory has him feeling “nuts in the best of all possible ways.” Karam was virtually unknown when the Roundabout decided to build its important 62-seat black-box theater in 2007 for his “Speech & Debate,” then commissioned his next play, “Sons of the Prophet,” and moved it upstairs to the main stage before it became a 2012 finalist for the Pulitzer Prize and won the New York Drama Critics Circle Award.

“Humans,” another Roundabout commission, opened there last October. And before the family tragicomedy-thriller was even reviewed, big-time producer Scott Rudin had committed to bring it to Broadway. “We were still tinkering on the play, just trying to make it to opening night,” says Karam in a phone interview from his Chinatown apartment, where he moved after the success of “Sons of the Prohet.” “I really couldn’t process it. It felt surreal.”

Surreal, also, is his pleasure at writing screenplays — an indie film of “Speech & Debate,” which, he says “has a lot of New York actors,” plus his adaptation of Chekhov’s “The Seagull,” staged by the Broadway theater director Michael Mayer, starring Annette Bening, Saoirse Ronan and Elisabeth Moss. He calls that “kind of a dream project, to be honest.”

Todd Haimes, artistic director of the Roundabout, says “Stephen’s career has taken the kind of ideal path that you wouldn’t believe if you read it in a play. We truly started the entire Roundabout Underground program because I so desperately wanted to produce his ‘Speech & Debate’ in an intimate space . . . Watching Stephen make a well-deserved Broadway debut, it strikes me that if you’re looking for a poster boy for turning an emerging playwright into an established one, he’s it.”

So who is this apparent poster boy, 36, who grew up gay in a working-class Maronite Christian family in Scranton, Pennsylvania, with a Lebanese-American father and an Irish-American mother? It wasn’t an artistic home life, but his parents always made him feel “supported with curiosity instead of judgment.” The Off-Broadway opening of “Humans” was their first time at one of his New York productions. “My dad doesn’t smile a lot,” he remembers fondly. “He’s an amazing guy, but not a laugher, not a smiler. I looked over and saw him smiling more than I ever saw him.”

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Karam, who went to Brown, jokes that he has “no elegant, classy stories” about his introduction to the theater. He “fell in love” with theater on school bus trips to “Phantom of the Opera,” “Miss Saigon” and other mass-audience mega-shows of the time. “It’s all very exciting when you don’t really know what’s out there . . . The little theater I was exposed to as a kid just felt special to me. I was a classic outsider, the theater nerd. I found a lot of great escape in it and started to read more and more plays.”

The Lebanese-American side of his family was the basis for “Sons of the Prophet,” a devastating, witty, subtle play about two motherless, fatherless gay brothers who happened to be distant relatives of the poet Kahlil Gibran. “The Humans,” beautifully directed by Joe Mantello, burrows into an Irish-American family, also from rust-belt Pennsylvania, with 90 minutes of overlapping wit, tenderness and blistering brutality.

He had intended to write a murder mystery, something he describes as “more genre. But I dug into a deep well and the psychology of the characters became too interesting, too complex, for their problems.” It is on Thanksgiving Day in the new basement-and-ground-floor Chinatown apartment shared by the family’s daughter and her boyfriend. We see both floors all the time, which gives the action what he has called a “dollhouse” view of the entire proceedings.

Before long, what he describes as the “existential horror and dread” make us realize this is no mere dysfunctional-family holiday play. “I’m not sure if it’s a genre collision — a family thriller. I took the most familiar thing in the world,” the Thanksgiving drama, “and I just bent it.”

In both “Sons of the Prophet” and “Humans,” a character is having what he calls a “medical struggle,” which relates to the autoimmune disease Karam has had since his teens. Anxiety over health insurance plays a central role in “Sons of the Prophet,” before Obamacare. He asks even now, “How did I live in a country where I need health insurance but I am not eligible” because of a pre-existing condition?

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Partly for the insurance, Karam worked for years as what he calls a “legal assistant” — “Making the coffee was my first task every morning.” He quit the day job when “Sons of the Prophet” was opening in Boston before New York and he was working on a chamber opera and realized he didn’t have “enough vacation days” left for his art. The play was a success and he realized he didn’t have to go back to the office.

To this day, he finds it “a little mysterious that the theater has always been my bliss. Still the impact of his Broadway debut didn’t really hit him until he was in the Helen Hayes. “That was the first time I really believed it. It actually felt real. There is something about being in a century-old theater in the middle of Times Square.” With no stars — at least not yet — on the marquee.