She said she had the surgery in July after trying to lose weight for a year after having a heart attack in 2012.
"I did it to save my life," she said during a luncheon sponsored by the American Heart Association.
She said she tried to get under 200 pounds per her doctor's instructions after her heart attack, but found it difficult to do with a healthy diet and exercise.
"She tried to lose weight on her own but it wasn't working," her spokesperson Cindi Berger told People.
"It was a life saving surgery," Berger said. "But it's only a tool, not a cure."
O'Donnell now weighs 190 pounds.