Talk show and media icon on Wednesday endorsed Vice President for president.
"What we're going to do is elect Kamala Harris as the next President of the United States," Winfrey said in a speech that drew a thunderous response from the Democratic National Convention crowd.
Winfrey also delivered a number of jabs at Republican nominee and his running mate, Sen. JD Vance of Ohio.
"We are beyond ridiculous tweets and lies and foolery," Winfrey said at one point.
Elsewhere in the speech, she referenced Vance's controversial remarks denigrating "childless cat ladies."
"When a house is on fire, we don't ask about the homeowner's race or religion. We don't wonder who their partner is, or how they voted. No, we just try to do the best we can to save them," she said.
"And if the place happens to belong to a childless cat lady, well, we try to get that cat out too."
Winfrey's speech night boiled the choice between Harris and Trump down to which candidate represents "the best of America."
"Very soon, we're going to be teaching our daughters and sons" about how Harris, the child of immigrants, "grew up to become the 47th president of the United States," Winfrey said. "That is the best of America."
"Let us choose the sweet promise of tomorrow, over the bitter return to yesterday," she said. "We won't go back. We won't be set back, pushed back, bullied back, kicked back. We're not going back."
"But more than anything else, let us choose freedom," she said. "Why? Because that's the best of America. We're all Americans, and together, let's all choose Kamala Harris!"
The appearance, which was reported by several news outlets earlier Wednesday but kept under wraps by the DNC, is notable not just for Winfrey's star power.
The influential media trailblazer has largely stayed above the political fray throughout her career, and "hadn't intended to be involved" in Harris' campaign, according to CBS host Gayle King, one of Winfrey's close friends.
Winfrey's first-ever endorsement of a political candidate went to then-Sen. Barack Obama in the 2008 presidential cycle. One study estimated that Winfrey's backing drove roughly into Obama's column in the Democratic primary.
She also supported former Secretary of State Hillary Clinton in the 2016 election and President in the 2020 cycle.
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