During an appearance on US journalist Katie Couric's new talk show on Monday she walked on stage in a fitted black dress and patent leather pumps for the big reveal.
"I've just had a lot of pressure on me to lose the baby weight," she said. "Today was actually one of my goals, getting here and just feeling comfortable in a beautiful dress, and I have to say I've achieved it, I feel beautiful today."
Simpson, who is now a mum to baby Maxwell, stopped short of announcing how much weight she had lost, but added, "I've lost enough weight to where I can pat myself on the back. It's a small child."
And the singer reveals not only did she find inspiration in her spokeswoman deal with weight loss company WeightWatchers, she has also been motivated to slim down for her upcoming season of Fashion Star.
She added, "I set small goals for myself ... I've lost weight every week, thank God, but I've worked really, really hard. I have to shoot a new season of my show Fashion Star, so I want to be in all the pretty dresses and the designer gowns. I'm 10 pounds (4.5 kilograms) away from that, so, by the time we're shooting, I'll actually be smaller, which is exciting."
Simpson admits that struggling to lose baby weight never really crossed her mind while she was pregnant.
"During pregnancy, I didn't really think about it," she told Couric.
"I thought my doctors were telling me that it was just a lot of water and whenever my water broke my whole entire stomach would go down but that did not happen. All the weight did not come out with the baby."
Simpson is committed to reaching her goals.
"I had to stay focused on my diet. I want to be as healthy as I can because I'm a mom now," she said.