How does actor Sam Waterston do it all? ‘I love to work.’

There’s the reboot of NBC’s “Law & Order,” in which Waterston reprises his role as venerable District Attorney Jack McCoy. There’s Hulu’s ” The Dropout ,” starring Amanda Seyfried as Theranos founder Elizabeth Holmes, in which Waterston plays Theranos investor and former secretary of state George Shultz. And this week, he’ll return as Sol Bergstein in the seventh and final season of “Grace and Frankie” on Netflix.

That’s how the actor explains appearing on three big television shows at once in 2022.

“You know, ‘Law & Order’ has been around a long time, so it can seem like an inevitability,” Waterston said of his second turn in the series, during a Zoom interview from his Connecticut home. “But who would have — I could never have imagined ‘Grace & Frankie’ coming.”

He was thrilled and even a little surprised to play the complicated Shultz, a powerful man who doubles down on trusting Holmes (she was convicted of fraud in January). “I don’t look remotely like George Shultz. It’s kind of amazing that somebody let me play that part. And I loved doing it.”

Waterston’s default, he admits, is to embrace as many opportunities as possible. “I love to work, so when people ask me, my tendency is to say yes.”

That philosophy is why Waterston, 81, took on another new role a few years ago. In 2020, he became chairman of the board of Oceana, a nonprofit founded in 2001 by a group of trusts and foundations (including the Pew Charitable Trusts and the Rockefeller Brothers Fund) with a mission of protecting the world’s oceans. He’d been on the board for years, but now runs meetings, works closely with Oceana CEO Andrew Sharpless, and, as Waterston put it via e-mail, tells “anyone who’ll listen how much we can do, and how responsive the oceans will be, if we just muster the will.”

(His acting and advocacy collided a few weeks ago in Los Angeles, when Oceana leadership and senior staff met outside at a restaurant, which happened to be in the shadow of a massive “Law & Order” billboard of Waterston as McCoy. “We all laughed about it and took pictures of each other in front of [it],” Sharpless said.)

Sam Waterston as District Attorney Jack McCoy in "Law & Order." Eric Liebowitz/NBC

Waterston knows his day jobs benefit his advocacy work.

“Celebrity gives you an opportunity to point out things that you think are important, and that’s an enormous boon,” he said. His role in “Grace and Frankie” made it a bigger deal when he was arrested in the fall of 2019 with Fonda as part of her Fire Drill Fridays, where she showed up on the steps of the US Capitol to draw attention to climate change.

“It’s all very well and good to stand up and make a speech ... and getting arrested with Jane Fonda as Sam Waterston was a fine thing to do. But the key thing is teamwork. I mean, the publicity tends to make it seem like, ‘Here comes a whole lot of famous people getting themselves arrested in Washington, D.C.,’ but it was a gigantic team with Greenpeace and all kinds of other organizations.”

Sam Waterston (center) and Jane Fonda (front left) during a climate change movement rally on Capitol Hill in Washington in 2019. Manuel Balce Ceneta/Associated Press

Born in Massachusetts, he traces his concerns about the environment back to his New England roots. His mother, Aliça, was an Atkinson.

“My mother’s family came over here in the 1600s. There’s an actual building in Newburyport — the cabin of the Atkinson family is still standing.”

He’s remained a New Englander. He lives on a working farm in Connecticut and keeps a home near Buzzards Bay, where he likes to spend some of the summer.

In January, he helped out the New Bedford Whaling Museum with its annual 25-hour marathon reading of “Moby-Dick” by kicking off a virtual reading of the book.

“He’s probably the biggest celebrity we’ve ever worked with, and yet was the easiest,” said Amanda D. McMullen, the museum’s CEO and president, adding that “he’s endlessly supportive to a number of organizations around here.”

Those who read the first pages of “Moby-Dick” to launch the event usually say its famous first line — “Call me Ishmael” — in a booming voice, said McMullen. But Waterston wanted the audience to feel like they’d just met this character in a tavern.

“He just sort of starts talking — and it’s like, oh my God, that’s what a pro does. It was amazing.”

After graduating from Groton School in 1958, he went on to Yale, where he studied theater, history, and French.

He performed off and on Broadway for decades, fitting in stage and screen as his resume grew. He was Nick Carraway to Robert Redford’s Gatsby in “The Great Gatsby” in 1974. In 1991, he starred with Reese Witherspoon in the coming-of-age film “The Man in the Moon.” Waterston’s “Grace and Frankie” cast-mate Martin Sheen said his favorite Waterston project is 1984′s “The Killing Fields,” about two reporters covering the Khmer Rouge regime in Cambodia. In it, Waterston plays Massachusetts-bred reporter Sydney Schanberg.

“He comes from a classic background,” Sheen explained. “I’ve seen him do Shakespeare, and he still plays in Shakespeare in the Park when he’s free. He takes on these enormous roles.”

Sheen and Waterston first worked together in the 1979 Western “Eagle’s Wing.” Now they play a couple on “Grace and Frankie”; their ex-wives are played by Jane Fonda and Lily Tomlin.

“His diversity [in work] is so much a part of his success — the longevity,” said Sheen of his screen partner. “I mean, we’re the same age, and he’s in a lot better shape than I am. And he did a Western [the Netflix series “Godless”] just a few years ago. I was astonished. He did this while he was on break from “Grace and Frankie.’”

The McCoy role on “Law & Order” came along in 1994. The show continued through 2010, and was syndicated, often running in binge-able marathons on cable, which meant generations got to know Waterston as the serious, level-headed enforcer.

Now, his role as Sol on “Grace and Frankie” has made him familiar to a younger generation. Sol on “Grace & Frankie” bears little resemblance to McCoy. He’s a sweet, sensitive character who does a lot of feeling his feelings. In 2019, Nylon ran a story exploring why “millennials love ‘Grace and Frankie.’” The same year, a “Saturday Night Live” sketch had Paul Rudd, DJ Khaled, and Pete Davidson performing a rap, pretending to love “Game of Thrones,” when really they were obsessed with “Grace and Frankie.”

“One of the stunning things about ‘Grace and Frankie’ is who watches — and it’s so many young people,” said Waterston. “Jane asks them, you know, ‘What are you doing watching this show about old geezers?’ ” he said, grinning.

In real life, Waterston has worked with young people on environmental causes.

“My favorite one is that I was on the sit-in protest at halftime at the Harvard-Yale game in 2019. And the students — who organize that thing and were nice enough to invite me to join them — were both from Harvard and from Yale,” he said. Their work, putting pressure on their schools to divest, was ongoing. “And guess what? Harvard first, and now Yale — come on Yale, catch up! — are divesting from fossil fuels.”

Oceana’s Sharpless appreciates Waterston’s commitment to the cause — and to balancing it with all his other work.

“He’s a very useful person. I mean, we should all be so useful. There’s not a cynical bone in the guy’s body, you know what I mean? He’s fully and enthusiastically committed to fighting the good fight and making the world a better place.”

Sam Waterston as Sol in "Grace and Frankie." Saeed Adyani

Sheen has similar observations about how Waterston approaches acting.

“There was a scene [in the first season where] he went to see [Tomlin’s character, Frankie] and tried to explain to her why he left her, and why he was in love with Robert,” Sheen says. “We had to look at that scene again because we were making reference to it now, seven years later. ... They’re outside sitting at an outdoor cafe, and he’s trying to explain why he was in the closet all those years, but how he didn’t love her any less. And the thing about the scene is that it is so heartbreaking. And at the same time it is hilarious. It is so funny. ... He doesn’t try to be funny, and he doesn’t try to be dramatic.

“He’s just ... he’s just honest. It’s about being honest.”

Meredith Goldstein can be reached at Meredith.Goldstein@Globe.com.