‘I think we have thousands of people inside of us,” says Judith Light. It’s a midsummer afternoon and Light – blond, patrician, beautifully manicured– is sipping a scarlet iced tea in a swanky midtown New York hotel. In a navy blazer and slim trousers, she looks too elegant to contain multitudes.

But Light is an actress of surprising versatility and astonishing skill. After conservatory training and a stint in repertory theatre, she became a soap star on One Life to Live and a sitcom star on Who’s the Boss? Two decades later, she won back-to-back Tony awards and a special Tony award earlier this year for her activism in support of the LGBTQ community and HIV/Aids programmes.

In the past dozen years, she has earned four Emmy nominations for series as dizzyingly varied as Ugly Betty, The Assassination of Gianni Versace: American Crime Story and Transparent. A longtime manager spent years telling her: “You need to let people know what else you do. They don’t know what else you can do.” Now they know.

‘I wish I could talk about it’ … Light, right, with Jeffrey Tambor in Transparent. Photograph: Alamy Stock Photo

Now, with the release of the Transparent musical finale, Light saying goodbye – maybe – to Shelly Pfefferman, the messy Jewish matriarch she has played since 2014, and hello to a complicated and mostly under-wraps character in The Politician, the new Netflix series from Ryan Murphy. She has one movie, Before You Know It, out in theatres now, and has been filming a miniseries, flying back and forth to Pittsburgh. There’s also a new series for Amazon, which must remain a secret, and a fresh producing partnership, involving a script from her husband, the writer and actor Robert Desiderio. She would like to do more theatre, but she doesn’t know when she’ll have the time.

Light is a graceful and animated conversationalist, who sometimes calls you “darling” and occasionally quotes Hugo and Kierkegaard and Eleanor Roosevelt. Her face, lightly made up, is beautiful and expressive. “I’m one of those people that Botox doesn’t work on,” she says. “No, no, I’m serious. I tried it.”

Back when the series began, Transparent’s creator Jill Soloway hadn’t thought of Light as a Shelly type; she didn’t know what she could do. “I was like, ‘No, Shelly is Jewish. Judith Light isn’t Jewish. She’s like a blond shiksa goyishe goddess,” Soloway recalls. But Light is Jewish. In fact, a casting director once told her she looked so Jewish, she would never work in the soaps. Light and Soloway had a Skype session and spoke mostly about their work on behalf of LGBTQ communities. Light got the part.

Transparent has afforded Light her latest renaissance, allowed her to flourish another of those thousands of people. She doesn’t want to think of the musical, which has just started streaming, as an ending. “I would call it a transition,” she says. I check with Soloway, who identifies as non-binary and prefers a collective pronoun. “We’re calling it the finale,” they say. “The name of it is the Transparent: Musicale Finale. It has the world finale in the title.” (Still Soloway hopes it might have another life. Maybe on Broadway.)

For four seasons, Transparent, which won a slew of Emmys and Golden Globes, centred on Jeffrey Tambor’s Maura. Born Mort, the character had married Light’s Shelly and fathered three children before revealing her gender identity and beginning her transition. Considered groundbreaking for its portrayal of the trans community and its championing of transgender actors and writers, Transparent made other, stickier headlines when an actress on the show and a former assistant both accused Tambor of sexual harassment. Tambor’s option was not renewed. He denies the allegations.

“It’s so difficult to talk about,” Light says, when asked about making the finale without Tambor’s Maura. “There is still sorrow. And there is difficulty. And it’s still – it’s hard to talk about,” she says. I ask about her work with Tambor, whose performance she had praised before the allegations surfaced. “It really is difficult to talk about,” she says. “And I’m – I wish I could, I wish I could, I just – I hope you understand.” And when Light looks at you – with her radiance, with the full force of her attention – yes, you understand. Or at least you stop asking.

Maura’s absence, courtesy of a convenient aortic aneurysm, meant that some else has to step into the spotlight. That someone is Light’s Shelly, a needy, meddling, achingly vulnerable Jewish mother, part of what Soloway calls “a forgotten generation of women who always feel like they’re waiting for their turn”. In the finale, Shelly takes it, which means that Light sings, she dances, she laughs, she cries, she gyrates in a flesh-coloured leotard and belts lyrics about shoving her grown children back into her vagina. And she inaugurates, to quote one of Faith Soloway’s envelope-pushing lyrics, “a joyocaust / For all the lives we’ve lost.”

‘So flexible’ … Light in Ugly Betty. Photograph: Karen Neal/Walt Disney Television via Getty Images

Light hasn’t performed in many musicals. The last one she did, Company, terrified her. She speaks of the Transparent musical as “a glorious creation”, praising her co-workers and somehow minimising her own efforts. Soloway isn’t so reticent. “She killed it,” Soloway says. “She’s like dancing her ass off and never tired. She never needed a break. We were just like, ‘What is she on?’ Can I please be that way when I’m 70? So flexible, so funny, so sexy.”

Light believes that actors are “investigative reporters, psychological investigative reporters”, and that acting is a service profession. She will sometimes conduct research into times, places, circumstances, accents. Shelly didn’t require much. Rather, the part meant giving voice and making space for a character she calls “so messy, and so all over the place, like an octopus with flailing arms”, and layering in the fragility and the vulnerability beneath all that flailing. Light felt for Shelly and allowed an audience to feel for her, too. “That’s the greatest gift that an artist can give,” she says.

Early in her career, she made more ego-driven choices, she says. “It was about me, about what was I gonna get?” she says. There’s nothing to get in life, there’s only what you give.” She doesn’t mean it in a saintly way, she says. That’s just how it is. “It’s like, give it all away! Give!”

Her activism, which she began in the 80s after filming a TV movie about Ryan White, an early Aids victim, is another kind of giving. Does she see a relationship between her advocacy and her acting? Light says that she doesn’t, at least not a conscious one. “I don’t think about it,” she says.

Sitcom star … Light with Tony Danza in 80s sitcom Who’s the Boss? Photograph: Craig Sjodin/Walt Disney Television via Getty Images

But her activism is based on the idea, as Light explains, that “we’re all of one family, we’re all human beings, we all can relate to each other in a way that is respectful and compassionate and honouring someone’s choice of who they know they are.” And she now chooses her acting projects with an eye to which roles might make a difference, spark conversation, sound an alarm, help us to see each other and our world more clearly and more kindly. Which are different, but not dissimilar ways of incarnating a better, kinder world and more authentic relationships.

These days, her authenticity involves mostly living in New York while her husband mostly lives in Los Angeles, though they visit each other often. It’s an arrangement they began while Light was filming Ugly Betty, and she is happy to proselytise. “It’s exciting,” she says. It’s vital. It’s independent, it is not co-dependent. We both love our alone time. Not everybody can do this, because you have to love your alone time, you really do.” Even the cat, who lives in Los Angeles, seems to understand.

At the beginning of her career, when she thought that taking a soap opera would demean her, when she thought that sitcoms weren’t where serious actors belonged, she didn’t imagine that at 70 she would be offered a life and an art that was so rich. That owes in part to an industry that is changing, however slowly, and now sees women over 40 as more than, as Light says, “the nutty grandma, or the kooky sister-in-law, or the bitchy head of the agency who had two episodes. It is not like that any more.” It also owes to women like Light and her peers insisting they are just as interesting and deserving of attention as anyone else.

Just before she leaves, Light quotes Helen Keller: “‘Life is either a daring adventure or it’s nothing.’ That’s the way I hold my life,” she says. “And within that is tremendous freedom. Doesn’t mean that fear doesn’t come up, doesn’t mean that all things work out the way you think you want them to. But it surely is a journey, an adventure, an aliveness that I would ever have expected.”

• Transparent: Musicale Finale is on Amazon Prime now.