One cool night in September, Eddie Vedder stood onstage at the Ohana Festival in Dana Point, Calif., looking out at a sea of expectant faces.

Vedder and his band the Earthlings had paused their headlining set so medics could make their way to an audience member in distress. Once the situation appeared resolved, he conferred with the band; they’d start again from the top.

“Uh, this one,” Vedder began to say — and then the Earthlings launched back into the song, taking their frontman by surprise and stepping on his reintroduction.

Vedder started singing, like a man chasing a bus as it pulls away. He stopped, grinned and let fly an expletive in the direction of his lead guitar player, a 33-year-old with a bleach-blond buzz cut who happens to be the producer of Vedder’s last solo album and the next one by Vedder’s other band, Pearl Jam.

The music clattered to a halt. Vedder, smiling but stern, pointed at the guitarist and began to admonish him for jumping the gun.

“This is Andrew Watt,” Vedder told the crowd. “He produces the records. But up here, young man? I’m in charge. I’m in control. I’m the boss.”

In the studio, it’s a different story. When he’s not playing live with Vedder — or as part of some other all-star outfit, like Iggy Pop’s backup band, the Losers, featuring the Red Hot Chili Peppers drummer Chad Smith and the Guns N’ Roses bassist Duff McKagan — Watt, born Andrew Wotman, is one of modern rock and pop’s most in-demand producers.

His first hits were songs for generational peers like Justin Bieber, Dua Lipa and Miley Cyrus. But he’s also become a first-call producer of new music by elder-god rock stars, working with performers so legendary they’re on a first-name basis with the entire world. Ozzy. Elton. Mick and Keith. Even Paul.

(Yes, that Paul.)

And although Watt would never put it this bluntly, sometimes a big part of that job is being unafraid to tell mythic musical icons what they should do. (Or at least — since another big part of the job is diplomacy — suggesting what might be cool to try.)

“This artist is working with a producer because they want to be produced,” Watt said in an interview at his Beverly Hills home a few months before the Ohana show. “If they’re showing up to do it with you, they want feedback.”

They’re rock stars, after all. If they live long enough, they usually start to second-guess themselves. They fall prey to self-consciousness, complacency, the creative consequences of festering internecine beef, or all of the above, and wander away from what they’re best at. Sooner or later, they need someone to step in and guide them back onto the path.

This is not the only thing Watt is good at, of course. In interviews, his collaborators praised his alacrity, his ability to communicate musician-to-musician, and particularly his unflagging energy. (Watt compares his in-studio demeanor to Richard Simmons, the relentlessly cheery ’80s exercise guru: “It might make someone laugh, or think I’m a maniac, but I’m me, and I’m genuinely happy to be there.”)

“He’s not one of those guys that gets in awe of people,” said Paul McCartney, who presumably knows awe when he sees it. “He just gets on with it.”

Elton John said he’s never seen anything like Watt’s presence in the studio, likening him to “a live wire.” “For someone of my age, it’s really, really infectious, and it’s really important that I feed off of someone like that,” he added.

“He takes every single session as seriously as if it’s Game Seven of the World Series and everybody is going to play like it’s Game Seven,” said the songwriter Ali Tamposi, a longtime friend who’s worked with Watt on some of the biggest songs he’s produced, including hits by Bieber and Camila Cabello. “He knows what to do and say to bring that out of everyone that he’s working with.”

But the most important asset Watt offers his clients, particularly those who’ve lived in the fog of their own legend for longer than he’s been alive, may be the encyclopedic enthusiasm of a fan who knows exactly what he’d want to hear on a present-day recording by his idols — and has the self-confidence to voice those preferences to their faces.

There is, after all, a crucial difference between “what you think other people want from you, versus what your fans really love about you,” said the singer-songwriter Brandi Carlile. Carlile, who’s worked with Watt on albums like John’s “Lockdown Sessions” from 2021, said Watt has a knack for helping wayward rock legends see their own light again.

“He has that in common with Rick Rubin,” she said. “They both have that ability to big-picture understand, culturally, how an artist has impacted the world, and bring them face to face with that. It might be his greatest superpower.”

As more and more iconic artists have sought out his perspective, Watt’s life has grown more and more unreal. Creative connections have blossomed into friendships. He talks to John every day. “Elton taught me about china,” Watt said. “Not the country — porcelain. The right plates, the right tablecloth. The right napkin rings. He’s a beacon of taste.”

(“I learned it from Gianni Versace,” John said, “so I’m passing it along to Andrew.”)

And Watt has spent so much time with Mick Jagger — in late 2022 and early 2023, while producing the Rolling Stones’ latest album, “Hackney Diamonds,” and during the long professional courtship that led to that gig — that sometimes, when the photo app on his iPhone serves him a slide show of his “memories,” the memories are of Mick Jagger.

In an interview, Jagger also praised Watt’s energy, crediting him with helping the Stones overcome the inertia that had kept the band from completing an album of new material since 2005. (The Stones and Watt are up for best rock song at the Grammys in February for that album’s single “Angry.”)

“He’s very enthusiastic,” Jagger said, “to the point of being too enthusiastic, sometimes.” At one of their earliest meetings, Jagger remembered, “I said, ‘Look, I can deal with this, but when you meet Ronnie and Keith, you have to dial it down a little bit.’”

WATT GREW UP in Great Neck, Long Island, but these days he lives in a spacious steel-and-glass house, surrounded by rock memorabilia. Even his art collection has a musical bent — it includes a clown painting by Frank Sinatra, a Warhol of Mick Jagger and a self-portrait in acrylic by David Bowie.

A visitor pointed out a photograph: a 13-year-old Watt onstage, on his knees, in dress shoes and shirt sleeves, soloing on a gold-top Gibson. It was taken at Watt’s bar mitzvah at the Copacabana in New York. The party’s theme was “Andrew Rocks”; he played Weezer’s “Say It Ain’t So” and Prince’s “Purple Rain.”

Watt smiled at the picture, an image of an inner child he’d done right by. “That,” he said, “is the most valuable thing in here.” (It was propped up between two Grammys.)

As a kid, he’d wanted to do nothing but play rock music; after dropping out of N.Y.U. to pursue it full-time as a solo artist, he struggled. But when he was offered a gig backing the Australian pop singer Cody Simpson, who was set to tour as Bieber’s opening act, he balked.

“I’m like, I don’t want to do pop,” Watt recalled. “I’m a rock and roller and I play in these nightclubs. Then they told me I would get $1,500 a week, and I was like, ‘I’m there.’”

Before shows, Watt would linger onstage after sound check, jamming to empty arenas for as long as the crew would let him. One day in Dublin, he began playing “Sunday Bloody Sunday,” imagining himself as part of U2. Suddenly, he heard drums. He turned, and saw Bieber sitting behind the kit. They jammed for 45 minutes without speaking, and a friendship was born.

Bieber and Watt began working on songs together. Two of Watt’s first production credits were bonus tracks for Bieber’s 2015 album “Purpose”; his first major hit as a songwriter and co-producer was “Let Me Love You,” with Bieber singing over a track by the French EDM producer DJ Snake.

Even after he’d demonstrated a knack for pop production, Watt plugged away at a career as a solo rocker; scroll far down enough on his Facebook page, and you’ll find a photo of a longhaired Watt signing a contract with John Varvatos Records, the music-mad men's wear designer’s Universal Music imprint, which released a Watt EP called “Ghost in My Head” in 2015.

“I went back to touring in a van and sharing hotel rooms,” Watt said. “The tour was costing me money out of pocket that I didn’t have.”

In November of that year, on the way to open for the British rockers the Struts in Reno, the van carrying Watt and his band hit a deer. They hitchhiked to the nearest phone, rode on each other’s laps in a tow truck, and made it to the venue in time to get heckled by Struts fans. Watt began to wonder what would be so wrong with pursuing pop production as a career.

Within three or four years, he’d built a Rolodex and a résumé, producing songs for Cabello, Bebe Rexha, Avicii, Rita Ora, Selena Gomez, 5 Seconds of Summer and Cardi B. But he’d also struck up a working friendship with Post Malone, whose music muddles rock, pop and hip-hop. In 2019, while making his third album, “Hollywood’s Bleeding,” Malone recruited Travis Scott and Ozzy Osbourne to guest on a track called “Take What You Want,” which Watt produced.

When this led to an offer from Osbourne to make an entire album together, Watt — who’d come to understand himself as a pop producer — balked once again.

“I love this music,” he remembered thinking, “but I don’t make this kind of music.”

He accepted the gig anyway, and together they made the 2020 album “Ordinary Man,” on which Osbourne — still recovering from health issues, including a broken neck — sounded both newly vulnerable and invigorated, as if he’d dined on fresh bat for the first time in years.

That album led to a second Osbourne album, “Patient Number 9” the next year, and to a Grammy for best rock album — and, in a broader sense, to Watt’s current position as rock’s premier boomer-whisperer, and therefore to days like the one Watt had last year, when a certain well-known guest came over for a cup of tea and a chat and Watt ended up writing an as-yet-unreleased song with Paul McCartney.

“He’s very resourceful,” McCartney said. “I said, ‘I’d like to show you something on guitar, but I haven’t got my guitar with me. And he said, ‘I’ve got a guitar.’ And I said, ‘Yeah, but I’m left-handed.’ He said, ‘Well, I’ve got a left-handed guitar.’”

They jammed, and McCartney returned the next day with lyrics and a vocal melody. “Suddenly,” he said, “we had a song. From a cup of tea to a song. Doesn’t it sound easy?”

(In a subsequent interview, Watt — who is left-handed in all things except guitar — admitted that he’d jolted awake in a cold sweat the night before McCartney’s visit, realizing that he had no left-handed guitars on hand, and began feverishly calling around until he found a friend to loan him a clutch of lefty Hohners, Martins and Rickenbackers, just in case a cup of tea led to something more.)

Watt still enjoys making pop music; over the summer he spent some time in the studio with Jung Kook, of the Korean pop juggernaut BTS. Jung Kook speaks some English, but not fluently, and Watt speaks no Korean. So he acted out what he wanted, they sang to each other, Watt did his Richard Simmons routine, and when the song was released in late July it went straight to No. 1.

The experience of walking into a room with practically nothing and coming out with a song never gets old, Watt said. But of course it feels different to share in the creative process of an Elton, a Mick or a Paul.

“There’s people in the industry who say to me, ‘Why do you work with people that are so much older than you?’ But I don’t care what anyone thinks,” Watt said. “I want to do what makes me happy. And getting to work with the guys who wrote the book — you get to learn so much. They still have so much to offer the world.”

“For a while,” Watt added, “I always thought I was born in the wrong generation. Like, ‘Man, if I was born when my dad was born, or a little after, I would be in some rock band now. And that would’ve been great.’ And recently, within the last year or two, my perspective on that has completely changed. And I feel I’m right where I’m supposed to be.”