For film actress Toni Collette to take on a television series, she had to be offered a dream role.

In the case of the new US series United States of Tara, it was really four roles in one that won her over - and convinced her to sign on for the next seven years. Collette plays Tara, a married mother of two who suffers from dissociative identity disorder, commonly known as multiple personalities. Her other personalities, or alters, are T - a wild, pot-smoking teenager, Alice - a prim and proper 1950s-style housewife, and Buck - a loud, profane Vietnam War veteran.

“I think as an actor you ache for something original and unique and exciting and provocative and confronting. As soon as I finished (reading the first episode) I knew I had to do it,” Collette said. “I have actually been offered a television show years ago which I was tempted to do and in the end I didn’t, because a series has to go on and I think that a lot of them really are like a one-trick pony effort. “With Tara the potential for the storylines is just un-ending.” The series, which is created by Diablo Cody (Juno) and has Steven Spielberg as executive producer, also stars John Corbett (Sex and the City) and Rosemarie DeWitt (Rachel Getting Married).

It aired in the US earlier this year and has its Australian premiere on the ABC on July 29. Collette researched DID extensively before starting the series and said she liked the way it normalised the condition, which is often brought on severe abuse or childhood trauma. “I think there’s a real beauty in acknowledging in these stories that they’re just like you and me,” she said. “I think that’s a really cool thing that Diablo’s done with Tara, she’s created a world that’s very accepting and that embraces something that maybe another writer would have written as taboo.”

Collette said keeping track of all her different roles was easier than it looks. “Each of the alters represent a certain aspect of Tara, so it really is just like playing one character... except who am I kidding, it’s not,” she said, laughing loudly. She said she couldn’t choose her favourite alter to play, comparing it to picking a favourite child.

T, who is very sexual and wears provocative clothing, was “surprisingly easy“, Collette laughs, but she was a bit nervous about playing Buck, a man. “I just didn’t want him to be a cliche. I think I’ve avoided that,” she said. “I just observed a few guys, they move differently and Buck is a real guy’s guy, too.” Collette, husband Dave Galafassi and baby daughter Sage will head back over to the US next month to start work on the second series of United States of Tara.

“It continues to be very exciting and almost shocking,” she said. “I have committed to it for seven years and I hope it does go for many years because we’re all really enjoying it.”

United States of Tara screens on Thursdays at 9.30pm on the ABC.