She was up to the task for most of the movie. But she admits that there was one scene that required so much hate that she almost fell apart. "There was one time that I got scared because I didn't think that my mind or heart could go to that place," the 40-year-old said.
But she pulled it off with a portrayal so searing, so devastating, that she's being touted as a possible Oscar nominee.
The dark urban drama, which debuted at January's Sundance Film Festival, won both the top jury prize and the award as the audience's favorite film. It opens in U.S. cinemas on Friday.
The film follows Clareece "Precious" Jones, an overweight, illiterate and abused Harlem teen who is pregnant with her second child. Precious, played by newcomer Gabourey "Gabby" Sidibe, is constantly discouraged by her mother, played by Mo'Nique.
The Lee Daniels-directed film - which also features Mariah Carey, Paula Patton and Lenny Kravitz - is being backed by Oprah Winfrey and Tyler Perry, who serve as executive producers.
In a recent interview, Mo'Nique talked about her role in the film, her recent weight loss and putting her "diva" ways behind her.
The Associated Press: You're known for making people laugh and Mary Jones is almost the complete opposite. How was it for you to play that role?
Mo'Nique: Rewarding. It was excited. It was challenging because I love to laugh, baby, I love to laugh. But it was appreciated because I don't know of any other director that would have given two fat, black women the opportunity to do what we did... The world needs to see it because guess what, Mary Jones exists, baby. So does Precious.
AP: How would you describe the film?
Mo'Nique: It is about a forgotten people. It is about obesity. It's about molestation. It's about cruelty. It's about HIV/AIDS. But it's about triumph - and that's the beauty of the movie. People say, "How do you walk away saying it's beautiful?" When you watch it and you understand, through it all, somebody can pick themselves up and keep it moving, that's beautiful... So I was proud to be a part of something that is very honest, and Lee Daniels, baby, he's going to give it to you. He's going to give it to you raw. No chaser, no lollipop licking, this is it. It's the dirt, it's the grime, it's what we're afraid of.
AP: Thinking about how Mary treated her own daughter - did that make you hate the very character you were portraying?
Mo'Nique: Reading the book, I disliked what she did. I won't say I disliked her, but I disliked what she did. Getting to that last scene of Mary Jones, I understood her. For as crazy as that sounds, you don't excuse it, but you don't want to judge it. Because it's easy to say that she's a monster, she's cruel, she's mean, but then who took out the time to say, "Well what happened to you, baby?" That's why I say they're the forgotten people.
AP: Did you leave the character on the set or did you ever take some of the baggage home?
Mo'Nique: I left it right there. I had to. And my husband, who is just amazing, Sydney, he said, "Don't judge it and don't take it off the set, walk away. When you're done, let it go..." It made me look at us differently. It made me look at mental illness differently. And it made me say, you know what, I could wake up the next day out of my mind, I would want somebody to say, "I give a damn. Come here. Let me get you some help."
AP: You've always been an advocate for "big girls," but you've dropped a lot of weight recently. What made you decide to slim down?
Mo'Nique: I feel amazing and it's not that I didn't feel amazing at 262, I didn't know that it was a problem. I didn't think it was a problem. I had people saying, "Girl, you look fabulous. Honey, you wearing that, baby" as I'm sitting there eating what I want to eat 'cause I'm fabulous, honey. I'm a star. I'm a sex kitten... Until my husband said that is too much, I want you for a lifetime... It gets you to a place where you get clear and you make a commitment you never thought you could make before. I never considered losing weight. I didn't think there was an issue. I'm like, baby, I'm fine, but now I've made the commitment to do it and (I'm) trying to get to 200 pounds.
AP: How have you seen yourself grow since your days as a young comedian?
Mo'Nique: There was a time that I thought it was about Mo'Nique and it took my best friends - my husband and two of my best girlfriends from elementary school to sit me down. They said, "We're getting tired of you now..." So I had to learn how to be considerate, to be a better friend. Because when stuff starts getting heightened, you can lose your way, but I'm glad I had the people in my corner to say, "Come here. You asked me for something, but you didn't say please. You trippin."'