WILLIAMSTOWN — Robert Sean Leonard wasn’t buying it.

Inside an airy upstairs rehearsal room at Williamstown Theatre Festival, in front of tall windows framing the distant Berkshire Hills, Leonard was trying to find his way through a moment in Act 4 of “Pygmalion.” Reprising a role he played to acclaim earlier this year at the Old Globe Theatre in San Diego, he was Professor Henry Higgins, having it out with Heather Lind’s Eliza Doolittle, who has decided to leave him. Something in the way Leonard had been asked to move across the stage struck him as false.

“It just feels a little theatrical,” he told Nicholas Martin, his director. “It feels a little un-Henry.” Also, the actor argued, this bit of the play truly belongs to Eliza, and he didn’t want to get in her way.

“I’m so happy to be upstaged,” Leonard said to Lind. “Because I think I should be, in that moment.”

The tale of a poor, uneducated young Cockney transformed into a model of elegance and elocution, George Bernard Shaw’s drama of class identity turns 100 this year. Williamstown is marking the centenary of its Vienna premiere by putting “Pygmalion” on the main stage, where it will run July 17-27.

“I now have a grotesque confession to make to you,” Shaw wrote in August 1912 to his old friend, the great British actress Ellen Terry. He’d written a new play for the stage star Mrs. Patrick Campbell, and he was certain it would suit her perfectly. But the role, as he described it, wasn’t exactly the sort to appeal to an actress’s vanity: “Liza Doolittle, a flower girl, using awful language and wearing an apron and three ostrich feathers, and having her hat put in the oven to slay the creepy-crawlies, and being taken off the stage and washed. . . . I simply didnt dare offer it to her.”

By the time “Pygmalion” opened in London in 1914, Mrs. Patrick Campbell was Shaw’s Eliza, and the play was a hit. It’s been part of the canon ever since. But when the Old Globe asked Martin to direct a new production, he wasn’t initially drawn to the prospect.

“I wasn’t excited about it at all — that’s how dumb I am, how little insight — until I got the idea that Bobby Leonard should play Higgins,” Martin said after rehearsal. A former artistic director at Williamstown and the Huntington Theatre Company, he’d directed the actor years before, and he knew he could cast around Leonard as the phonetics professor.

“You need to have an actor in that part who has enormous facility with speech, with articulation of the part, with a really high intelligence, and, from my point of view, with a sex appeal that he doesn’t necessarily — the character — know he has. In other words,” Martin said, “you need a kind of star. But the pool of actors who [are] trained enough and smart enough and good-looking enough and not even so much good-looking but charismatic enough to play that role are very few.”

At Williamstown, the cast is almost entirely new since San Diego. Paxton Whitehead, whose Shaw credentials include having spent a decade as artistic director of the Shaw Festival in Ontario, played Higgins’s fellow bachelor, Colonel Pickering, at the Old Globe and is doing so again at Williamstown. He’s had that role, too, on Broadway in “My Fair Lady,” Lerner and Loewe’s musical adaptation of “Pygmalion.”

For Lind, who played the daughter of Al Pacino’s Shylock in the 2010 Broadway revival of “The Merchant of Venice,” this is the first time as Eliza, a young woman who leaves her own culture to enter another, living with Higgins and Pickering as the professor labors to “make a duchess of this draggletailed guttersnipe.”

“It’s a frightening story, it really is, and it’s frightening to experience — disorienting,” said Lind, who senses “a kind of homelessness” about Eliza through much of the play.

“She has nowhere else to go but with these men, who’ve sort of stripped her of her boldness in some ways,” she said. “Because suddenly she’s a person who’s obeying rules. Linguistic rules, but nonetheless.”

To Martin, “the most exciting thing” about the production aside from Leonard’s presence in it has been discovering Lind. “She’s in every way his equal,” said Martin, the director of this year’s Tony winner for best play, Christopher Durang’s “Vanya and Sonia and Masha and Spike.”

Leonard spent eight seasons, from 2004 to 2012, on Fox’s medical-mystery drama “House M.D.,” playing Dr. James Wilson, buttoned-up friend to the chronically rule-breaking title character. But onstage, he seems most comfortable in eras earlier than this one. He won a Tony in 2001 for playing the young A.E. Housman in Tom Stoppard’s “The Invention of Love,” and his most recent Broadway outing, two years ago, was Garson Kanin’s “Born Yesterday,” from 1946.

“I think I’m better in period plays,” the actor said. “I like lace-up shoes.” He recently journeyed back to the Depression-era South, playing Atticus Finch in a London production of “To Kill a Mockingbird.”

“I’m an old-fashioned guy,” Leonard said. “I’m sure Adam Rapp is a wonderful playwright. I’m sure there are young, great playwrights. I’ve just — I don’t know them. I’m too lazy to know them. I know O’Neill and Brian Friel and Tom Stoppard and Shakespeare and Shaw. I have a lot of great playwrights. They’re all just dead, except Tom.”

Leonard, who recalls a star-struck moment as a teenager, watching Kevin Kline in Shaw’s “Arms and the Man,” said he has no interest in what he calls “muscle theater.”

“I didn’t grow up with Steppenwolf,” he said. “I didn’t grow up with theater of emoting. So I think I tend to gravitate toward proscenium, five-act Shaw.”

Even so, he said, Martin was the reason he considered playing Henry Higgins.

“It’s a role I never wanted to play,” said Leonard, his notion of Higgins having been shaped by Leslie Howard, star of the 1938 film “Pygmalion,” and Rex Harrison, from the 1964 movie “My Fair Lady.” “But I read it, just to be nice.” In Shaw’s text, he was surprised to find a character who’s rude, sloppy, and dismissive enough to alienate his mother’s friends in her own home. “Anyway, I thought, maybe he’s sort of like the Robert Downey Jr. of his time. Maybe I’ll try to make him not quite so natty.”

For Lind, whose impression of Eliza had been colored by Audrey Hepburn in the movie “My Fair Lady,” the darkness of the play was a shock. But Eliza’s tremendous arc has thrilled the actress, and she savors the words Shaw wrote a century ago for her character to say to Higgins at the end.

“I get to say, ‘Oh, when I think of myself crawling under your feet and being trampled on and called names, when all the time I had only to lift up my finger to be as good as you, I could just kick myself.’ I mean, I’ve walked away from relationships wishing I had had that kind of language,” Lind said.

It’s exciting — inspiring, even — to be that communicative, and that vulnerable, she said.

“Their relationship is a little fraught,” Lind laughed, “but I kind of admire it.”