Josh Groban says one of his adolescent dreams was to be middle-aged. No, really. “I couldn’t wait to be 40,” he recalls. “I was an 18-year-old kid who couldn’t wait to have that gravitas. Because my voice was big but I was not. And I loved the roles that were bigger, darker. More aged.”

That does help explain why he was in such a rush back then, leaving theater school at Carnegie Mellon University in his freshman year to embark on a recording and concert career, one that shot him out of the gates like an odds-on favorite at Churchill Downs. With a sumptuous baritone, a yen for show tunes and standards, and a nerdy handsomeness that many a mother could love, he amassed all of the tokens of singing star success: Grammy and Tony nods, multiplatinum albums, sold-out world tours.

The fame and money came a lot faster than did 40. But that finally happened, too — on Feb. 27, 2021, to be exact. Having successfully conquered that chronological goal, the now 41-year-old Josh Groban has been looking for other hurdles befitting a person with a zeal for midlife advancement. Offbeat movie roles. A guest slot in Lin-Manuel Miranda’s “Freestyle Love Supreme.” And that capstone affirmation of artistic maturity: a lead in a Sondheim musical.

And not just any lead, but one of the most coveted in the canon of the late Stephen Sondheim: Sweeney Todd. On Thursday, Groban will start rehearsals alongside Annaleigh Ashford (as the redoubtable Mrs. Lovett) in the third Broadway revival of “Sweeney Todd, the Demon Barber of Fleet Street” since the 1979 original that starred Len Cariou and Angela Lansbury. The director is Thomas Kail, who shepherded to Broadway the most influential hit of the past two decades, Miranda’s “Hamilton.”

Groban is materializing in parts both whimsical and tailor-made these days: as a waiter in “Weird: The Al Yankovic Story” on Roku; as the Beast opposite H.E.R. in “Beauty and the Beast: A 30th Celebration” on ABC. “Sweeney Todd,” with a score by Sondheim and a book by Hugh Wheeler, is a far bigger deal. It ticks off a lot of boxes for a guy whose more serious ambitions have been fixed toward bigger and darker.

“I’ve thought about it,” Groban says, “ever since I was a camper at Interlochen.” (That’s the highly regarded training center for the arts in Michigan he attended in the 1990s — and where he lost out one summer on playing Sweeney.) “You know, I’m not one of those people who just wants to shoehorn something in just because it’s something I love. So it had to be right.”

In the coming months, audiences at Broadway’s Lunt-Fontanne Theatre, where “Sweeney” is set to begin performances on March 26, will judge whether Groban is right for it. The voice being a match for the music is a given. But can this preternaturally genial fellow plausibly play the serial revenge killer of this blood-soaked musical? In the past, Sweeney’s been the Broadway property of brooding types such as Len Cariou and Michael Cerveris, the latter starring in a 2005 revival opposite Patti LuPone, and of course, Johnny Depp in the 2007 film version.

Groban is a performer with a sunnier stage temperament; he’s a pleaser who slips easily into lighthearted assignments, as, for instance, co-host of the Tony Awards (with Sara Bareilles in 2018).

On the question of whether Groban can satisfactorily deliver a Sweeney with gravitas, though, Kail has no doubts. “When Josh plays Sweeney, it’s an exploration of a Sweeney who had a light and how that light gets extinguished,” the director says. “How his Sweeney encounters the world when so much has been taken from him. It’s what he brings to it instinctively, full-throated-ly.”

Six years ago, Groban made his Broadway debut in a head-turning production that suggested an artist who could zig when the world expected him to zag. In “Natasha, Pierre and the Great Comet of 1812,” a musical directed by Rachel Chavkin and adapted by composer Dave Malloy from “War and Peace,” Groban played lumpy, taciturn Pierre in a padded costume and sang the plaintive “Dust and Ashes.” It earned him a Tony nomination and the gratifying feeling of being accepted into an ensemble.

“I was very spoiled by the ‘Great Comet’ experience, because it started so organically,” he says, sitting in the Lunt-Fontanne on the autumn day he was visiting it for the first time. Groban had seen the musical in its original, off-Broadway incarnation, loved it and decided to try to make something happen. “I reached out at the exact same time they reached out, and it was like, ‘Oh, he’s interested. Well, we were just going to ask him anyway.’ And I went out and got, you know, three pints with Dave and Rachel. And we talked about the role and it was like, ‘Let’s workshop it,’ and then it just happened naturally.”

That appetite strikes those who know him as classic Groban. “Frankly, there’s an easier path for Josh Groban, the version of Josh Groban who has a residency in Las Vegas or is smiling in soft focus on an album cover, but that’s not who he is,” says his friend, comedian Alex Edelman. “He makes hard and interesting career decisions. He pushes himself in really challenging directions.”

The path to being Josh Groban at 41 involved some trial, error — and terror. As he describes it, the success was so meteoric that he really wasn’t able to digest it. All the work and pressure of grueling concert tours made him a nervous, joyless wreck. “By the time I was 25, I was having an existential crisis,” he recalls. “I had already released three albums. You know, I sold 20 million records at that point. And I was thinking to myself, ‘Well, maybe that’s it.’ I’m 25 and thinking to myself, ‘It can only go down from here. Maybe I’ll be a veterinarian.’”

What looked from the outside like a carefree climb was in fact a perpetual steppingstone to anxiety. “You’re technically being thrown all these extraordinary experiences, but you’re seeing them through a real narrow lens of appreciation of those experiences, because the pressure is so great,” he says. “So you’re seeing the world through a hotel window, you’re experiencing the cuisine through room service.”

Maturity, to Groban, entailed letting himself off the hook. Instead of giving up, he decided to try finding some balance. “At some point, I stopped thinking about proving it and I just started to enjoy being able to live in it and say, ‘Okay, you’ve done a lot. You’ve accomplished a lot. Now, have fun, enjoy what you’ve done, but also have fun taking risks.’”

It’s a philosophy he’s attempting to employ again, in “Sweeney Todd.” He and Kail talked about the project before the pandemic and then returned to the notion in November 2021, when they organized an informal session in New York to sing through the musical. Two days before it was to occur, Sondheim died. “We were all of course just shellshocked,” Groban says. “We all kind of huddled and said, ‘Do we do this?’”
The answer ultimately had to be yes. “To feel like we get to honor him this way, and to know that this was something he wanted to have happen, is something that we take very, very seriously.”

Groban envisions a Sweeney Todd who was a hard worker and family man who might have had an ordinary life until monstrous injustice twists him into something hideous. “I find it so much scarier,” he says, “when you can follow the man becoming the demon.”

This bigger, darker Broadway opportunity is something Groban is eager to grab. “All I’ll say,” he adds, “is I’m in it for as long as people will come.”