Oprah Winfrey, in a Convention Debut, Calls Harris ‘the Best of America’

The television legend Oprah Winfrey returned to prime time on Wednesday in a surprise appearance at the Democratic National Convention, calling on Americans to choose “optimism over cynicism” and “inclusion over retribution” as she endorsed the candidacy of Vice President Kamala Harris, whose life story Ms. Winfrey deemed “the best of America.”

Ms. Winfrey, a billionaire media mogul who built her career in Chicago, had never before spoken at a national convention. Her speech was carefully kept under wraps by Democratic organizers, including a cloak-and-dagger act during rehearsals in which one of the most famous women in America crept into the United Center wearing a hat, sunglasses and a face mask.

When Ms. Winfrey said hello to Representative Nancy Pelosi of California, Ms. Pelosi had no idea who she was at first, according to Ms. Winfrey’s friend Gayle King, the CBS anchor.

The obvious excitement in the crowd when Ms. Winfrey emerged on Wednesday evening was a reminder of her power as a public speaker and a widely recognized icon of optimism, particularly among the female and Black voters that Ms. Harris is hoping to turn out in big numbers on Election Day.

Ms. Winfrey’s speech touched on school integration, the preservation of democracy, and civil rights icons like John Lewis. Dressed in a purple outfit, she appeared to direct her remarks toward the country’s political independents, a cohort to which she said she belonged.

“Decency and respect are on the ballot in 2024, and just plain common sense,” Ms. Winfrey said, before building to a climactic passage that evoked the energy of her daytime talk show, which ended in 2011.