"It's really enjoyable, I love doing it - it's a great challenge," she told AAP.
The second woman to be appointed to the US Supreme Court, Ruth Bader Ginsburg - or RBG as she became known - was a trailblazer and advocate for reproductive rights and women's equality.
RBG: Of Many, One, by Olivier Award-winning Australian playwright Suzie Miller (Prima Facie) charts RBG's teenage years in New York, her historic Supreme Court nomination and her work during the Clinton, Obama and Trump administrations.
Sound dry? The play's initial eight-week season at the Sydney Theatre Company's Wharf Theatres in 2022 was a sellout, drawing standing ovations and rave reviews.
An encore season at the Sydney Opera House opens Tuesday, before the launch of a national tour to Parramatta, Wollongong, Canberra, Melbourne, Brisbane and Perth.
As for all the characters Mitchell plays in the one-woman show, there's not only RBG herself (between the ages of 13 and 87) but her husband and granddaughter, as well as presidents Clinton, Obama and Trump.
Mitchell plays the late Supreme Court judge and other characters in the one-woman show. (HANDOUT/SYDNEY THEATRE COMPANY)
It's perhaps because of all these various voices that Mitchell says she never feels alone onstage, revealing she once expected another actor to deliver a line in a scene between RBG and Bill Clinton.
"I was delivering a line as Ruth and then I was waiting, I thought the other actor had forgotten their line, and then I went 'oh, that's me!'" she laughed.
"So I thought wow, I actually think there's someone else out there with me."
Ruth Bader Ginsburg died in 2020 at the age of 87 while she was still in office.
The vacancy she created was filled just over a month later by conservative judge Amy Coney Barrett, part of a historic shift to the right by the highest court in the US.
RBG had been asked to retire years earlier, ensuring a Democratic president and Democratic-controlled Senate could appoint and confirm her successor, but she refused.
Mitchell used to feel strongly that RBG had every right to remain as a judge despite the broader consequences, but these days she is more ambivalent.
While the show is about the US judicial system it has much to say to an Australian audience, according to Mitchell, with reflections on democracy, equality and progressive causes.
The play's initial eight-week season in Sydney in 2022 sold out and received rave reviews. (HANDOUT/SYDNEY THEATRE COMPANY)
Directed by Priscilla Jackman (White Pearl, Still Point Turning), the majority of the team behind the return season of RBG remains the same as in 2022.
Heather Mitchell, for one, feels it's an honour to return to a character she loves.
"It's great to have the privilege of being able to keep her words alive, her messages and the things that she believed in," she said.
RBG: Of Many, One opens at the Drama Theatre, Sydney Opera House on Tuesday, and runs until March 30.
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