"I told everybody who knew me if he ever ran, I would put everything I had at stake to support him because there's a wonderful Bible passage that says 'What does it do to gain the world and lose your soul?'" she said. "And I knew that in this moment in time, in my lifetime, I would have lost a piece of my soul had I not stood up for him. So I'm happy I happen to be on the right side of history. But if this had not turned out the way we all wanted it to, it was still the right thing for me to do in the moment I did it."
Asked by Roberts if she can take credit for helping him win, Winfrey was quick to reply, "I'm certainly not responsible."
A December ABC/Washington Post poll backed up Winfrey's assertion. Only 8 percent of Democrats said they were persuaded by her Obama endorsement, 82 percent said it wouldn't matter either way and 10 percent said her recommendation had turned them off Obama.
Winfrey also shared with Roberts her experience of voting early last week. Winfrey struck up a conversation with some women at a drug rehab center across from her polling place. "It was great," she said, "great because for many of them it was the first time voting and they were proud, proud to be there. And I thought, 'Listen, we'll take the drug addicts' vote.'"
Here's what some other celebrities had to say about President-elect Obama:
Tina Fey, who brought some of the highest ratings to "Saturday Night Live" with her Sarah Palin impersonations, talked about the experience on Thursday's Oprah Winfrey Show.
"I'm really happy I did it," she said. "It was a wonderful chance to go home again and be with my friends at Saturday Night Live."
But, now that the election is over, so are Fey's days playing Palin. Fey told Oprah: "I think I'm going to pack up my wig."
Singer Beyonce vowed the day after Obama's victory to be at his service.
"I'm there. I can't wait. I feel like all of us, we're ready to do whatever we have to do," she told the Associated Press. "Whatever they want -- if they need me to volunteer, they need me to sing, I'm there, and I'm ready. I've never been so patriotic!"
After going with hubby Jay-Z, Diddy, Mary J. Blige and others to states like Pennsylvania, Florida and Ohio just before the election, Beyonce watched the returns Tuesday night with family and friends in her home.
"I fell asleep crying and smiling at the same time," she laughed. "I woke up with mascara running and a smile on my face!"
Will Smith grew teary on the set of the Oprah show Thursday while discussing Obama's win. "I was raised to believe that that could happen," Smith told Winfrey. "Nobody is better than you and anything you want, you set your mind to it and you go for it period. I've always carried myself as if I was deserving of that position. The history of African Americans is such that you want to be part of America, but we've been rejected so much. At that second, at that moment (that Obama won), all of our excuses were gone."
"I was done," Smith said about the moment Obama was declared victor. He rolled around Winfrey's stage to demonstrate just how overcome with emotion he was. "My daughter was sitting on my lap, Jaden was sitting beside me, holding my hand and Trey was standing behind me. Barack gave his speech and I just lost it."