Michelle Williams on Playing Marilyn Monroe: 'I've Found My Voice'

Michelle Williams says playing Marilyn Monroe has changed her life.

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"I feel like something has changed for me...Maybe it has something to do with turning 30. I don’t feel as shy or nervous or self-conscious. I have more confidence that I can handle what life brings me...It's like I've found my voice," she tells the October issue of Vogue, which hits newsstands on Sept. 20.

STORY: Simon Curtis' 'My Week With Marilyn' to Premiere at 2011 NYFF

"I wish that I could play her for the rest of my life," adds Williams, who says the role has helped her move past Heath Ledger's 2008 death (they are parents to Matilda, 5).

"Three years ago, it felt like we didn't have anything, and now my life -- our life -- has kind of repaired itself," she says. Ledger's death, "changed how I see the world and how I interact on a daily basis. It's changed the parent I am. It's changed the friend I am. It's changed the kind of work that I really want to do. It's become the lens through which I see life--that it's all impermanent."

For the film, Williams was unsuccessful at gaining weight, so instead used foam padding.

"Unfortunately, it went right to my face," Williams tells Vogue. "So at some point it became a question of, Do I want my face to look like Marilyn Monroe's or my hips?"

Debuting a new body "felt like being reborn. It felt like breaking my body and remaking it in her image, learning how she walked and talked and held her head. None of that existed in my physical memory, and I knew I needed as much time as possible to make it part of me," she says.

My Week with Marilyn is due in theaters on Nov. 4.

Annie Leibovitz