Since shooting to fame 10 years ago as an alien trapped in the body of a leggy blonde earthling in the American sitcom 3rd Rock from the Sun, Kristen Johnston has worked hard to put her extraterrestrial past behind her. The past five years have been devoted to the New York stage, with television appearances restricted to a Sex and the City cameo and six episodes of ER. "Now, when I'm walking round New York, people know my body of work so that when I'm recognised I feel like, 'It's OK, I've worked really hard'," she says. "But to be known only as an alien? It felt similar to being picked on because I was tall. It felt that I was being looked at as a freak." While the 39-year-old actress might feel more comfortable in her own skin these days, at 6ft, with blonde hair piled up messily on top of her head making her even taller and a voice that heralds her arrival long before she bursts in and grabs my hand, it's hard to ignore her imposing physical presence.
We meet as Johnston prepares to make her West End debut in John Kolvenbach's Love Song. The playwright has reunited with the director John Crowley in attracting a constellation of big names - Cillian Murphy, Michael McKean, Neve Campbell and Johnston. Perhaps mindful of the Old Vic's ill-fated Resurrection Blues, and ever ambivalent about fame, Johnston is quick to deny the suggestion that she is just "some star coming across the pond".
Johnston plays Joan, wife of Harry and sister of Beane (Murphy), an oddball loner who begins a relationship with the mysterious Molly after a burglary at his flat. Molly acts as the catalyst for the characters to reassess their intertwined relationships and to open up to their fantasies. "They're two very damaged people - Joan chose one road, which was to be a control freak and deal with everything with cold, calculating venom," explains Johnston. "And then there's her brother who has chosen to isolate himself." Johnston's challenge is to take Joan from a domineering loudmouth to a gentler human being. "You can't just be this [she pulls a terrifying face] raging lunatic. She has to come from a place of being emotionally hijacked and not understanding her own feelings."
Growing up in Milwaukee, Johnston dreamt of appearing on the London stage but was far from being a child star. "I did do school plays, but I was bad in them. I wasn't precocious and my mother was not a stage mother and could barely drag me to lessons." Throughout her childhood the attention was focused on her older brother's talents as a classical musician ("My mother was actually very stage-mothery about him," she muses). Johnston went on to study drama at New York University before making her debut with David Mamet's Atlantic Theatre Company.
Throughout the early 1990s, she was a "theatre company whore", also appearing in the Lincoln Center's The Lights, for which she gained a Drama Desk nomination, and with The Naked Angels, where she first met Sarah Jessica Parker. Fourteen years on, the friendship led to Johnston's memorable cameo in the final series of SATC as Lexi Featherston, the faded, coked-up It-Girl, who is condemned to death-by-Manolo. At a party attended by Carrie et al, she announces, "I'm so bored I could die," before tripping on her vertiginous stilettos and hurtling out of the window. "They wanted a stunt woman and I said: 'It has to be me.' The physical stuff is what I love," says Johnston proudly.
It was presumably her gift for the "physical stuff", along with her height and husky voice, which caught the eye of the 3rd Rock producers back in 1996.By the time it came to an end in 2001, six series and (for Johnston) two Emmys later, she was "dying to stop". She turned down some "reeeevolting" projects and, unimpressed by the burgeoning celebrity culture, turned her back on Los Angeles, much to the annoyance of the television execs. "They get mad and then they start punishing you," she tells me conspiratorially. "They can't believe anyone would not choose fame and money... I don't regret doing 3rd Rock because it changed my life in many ways. But choosing this life instead of that life is something I'm proud of."
Ever the canny operator, Johnston kept her options open throughout her stint on television, reasoning, "I'll never have that fame again and I'd never had it beforehand." In the annual four-month break from filming, she raced back to New York to appear on stage. She walked straight from 3rd Rock on to Broadway to star in a revival of the 1936 comedy of manners The Women alongside SATC's Cynthia Nixon, Golden Girl Rue McClanahan and Jennifer Tilly. She moved back to New York on 10 September 2001; the events of the following day cemented her determination to stay and she has thrown herself into the city's theatre scene ever since.
Her all-time favourite role came with 2004's Shakespeare in the Park, playing Beatrice to Jimmy Smits' Benedick in Much Ado About Nothing. Shakespeare's feistiest, funniest heroine met her match in the larger-than-life comic presence of Johnston, described by one critic as "born to play Beatrice". During the run, she was spotted by the television producer John Wells who gave her the choice of new roles on either The West Wing or ER. She plumped for the "evil nurse", Dr Eve Peyton, bursting into County General wielding fiendish staffing schedules and a ball-busting line in put-downs. It must have been a blast to play. "They're much more exciting to watch than to do," she demurs. "It was just sort of boring."
A case of one tough girl too many, perhaps? "The one part that I really relate to is Beatrice - who is tough and a feminist herself but is also a total woman," she says. "The part on ER I took unseen. Is it fun to play the person who everyone rolls their eyes at behind their back? Yeah it is, but it's not as fun as playing someone whose malevolence is a little trickier. That's what I would prefer. Being just a bitch is not that fun to me."
Her next film, Music and Lyrics By, is a rom-com in which she stars as Drew Barrymore's sister and a crazed fan of a washed-up Eighties rock star played by Hugh Grant. She hopes it might reveal her more feminine side. "She is a sweet, funny goofball. That's the way I see it, but sometimes I'll see it one way and it'll come off as ballsy and tough because I'm playing it."
As she edges towards 40 ("I can't believe I just turned 39. I feel so young. I still wear sneakers," she says), Johnston seems ready to soften up. While she flatly refuses to talk about a partner, she hints at a desire to settle down and have a family. In the meantime, her spare time is taken up with walking her two dogs, reading, decorating her country house in Connecticut and taking up painting again. "I'd like my life to be about something else but for a long time [acting] was my friends, my family, my creative outlet, my income, my everything. I do think it's now taken a more relaxed and realistic place in my life - it's a job, but it's a fun job."
'Love Song', New Ambassadors Theatre (08700 606 627), 4 December to 3 March