Vice President Kamala Harris will appear with Oprah Winfrey on Thursday evening at a campaign event in Michigan, leveraging one of her most influential surrogates to reach out to voters in a crucial battleground state and beyond.

The two are scheduled to headline a virtual event, “Unite for America,” which will be held in an undisclosed location in a Detroit suburb. There will be a small in-person studio audience, which will be streamed online.

The event will feature representatives from some of the dozens of online groups that have coalesced around Ms. Harris since she became the Democratic nominee, including “White Dudes for Harris,” “Cat Ladies for Kamala” and “Latinas for Harris.”

Ms. Winfrey is hosting the event in collaboration with “Win With Black Women,” which was the first group to draw tens of thousands of people to a Zoom fund-raiser for Ms. Harris after she entered the race, inspiring some of the other groups that followed. The group’s founder, Jotaka Eaddy, will join Ms. Harris and Ms. Winfrey at the event. Gov. Gretchen Whitmer of Michigan is also expected to attend.

Ms. Winfrey endorsed Ms. Harris last month, and gave a full-throated speech on her behalf at the Democratic National Convention, her first time addressing a party convention. In her speech, Ms. Winfrey called on Americans to choose “optimism over cynicism” and “inclusion over retribution.”

“Decency and respect are on the ballot in 2024, and just plain common sense,” Ms. Winfrey said.

Ms. Winfrey’s endorsement is a coveted one, as she has largely shied away from politics, reserving her influence for a few major races. In 2007, she endorsed then-Senator Barack Obama for president, and hit the campaign trail for him in Iowa.

Ms. Winfrey said she wanted to use Thursday’s virtual rally to motivate people to go to the polls.

“What is essential to me is getting people motivated to vote — and that’s my intention in hosting this event,” Ms. Winfrey said in a statement announcing the event. “My goal is to get people excited about the privilege and power of the vote.”