In a new interview the actress gives a rare insight in her personal life, telling how her "naughty" behavior while she was off set could have easily made it impossible for her to work in Hollywood.
"There was a lot of goodwill for me in Hollywood," she says during an interview for the March issue of Esquire magazine.
"I think I’d been lucky in that I’d always been naughty in that town and people had always liked me for it. (But) I sabotaged things. I burnt a lot of bridges. I never read a review or paid any mind to what anyone said."
"And that translated to how I behaved outside work. On set, I was first to arrive, last to leave, best friends with the crew, totally professional.
"But when I wasn’t at work, I wasn’t behaving the way you should. I’m very lucky to have a second chance in that town. What was going on in my private life was not an easy thing to read about. People don't want to see films with people they don't approve of in them."
The interviewer asks her: "But it's not like you've actually done anything immoral, have you?" She replies: "No, no, no, I have."
Sienna shot to fame after appearing in Layer Cake with Daniel Craig in 2004. she was only 21 at the time, and – she says – not wise beyond her years at the time.
"I was really naive, I think. I was a young 21," she says. "Not green as grass – I was by no means an innocent – but I had faith in the goodness of everyone.
"I was very open. And that led me into all sorts of situations that backfired."
Sienna's much reported relationship with Jude Law came to an end after claims he had been unfaithful. She went on to date Balthazar Getty, who was married at the time and has four children. There have also been claims she was romantically involved with James Bond star Daniel while they were filming Layer Cake and were both in relationships with other people.
Rocky personal relationships are a thing of the past for Sienna, however. The star is blissfully happy with Tom, who she is engaged to marry.
"I feel really settled. I have a wonderful life. I'm up every morning with a little baby," says of the couple's 18-month-old.
"That gives you incredible perspective. It's such a gift. And it's grounding in a way you can't describe."
Of Tom, she says: "He's the antithesis of me, really. And that's a first for me, to be in a relationship with someone who's in a lot of respects very different. He's the perfect balance to my lunacy, which makes him sound really boring, but he's not, at all.
"It's good, it works. It's not easy, of course, but we're a family and I love that. I wake up and I'm like, 'I'm a family, I'm a grown up!' I still can't believe it."