The Democratic National Convention is expected to feature speeches from at least three Republicans, with a Republican hosting the convention’s second night, as Vice President Kamala Harris’s campaign seeks to highlight opposition to Donald J. Trump from within his own party.

Former Representative Adam Kinzinger of Illinois, who swept into Congress as part of the Tea Party wave of 2010 and then became one of the most vocal Republican opponents of Mr. Trump, then the president, after the Jan. 6, 2021, attack on the U.S. Capitol, will speak later in the week, according to a Republicans for Harris campaign official.

Ana Navarro, a Republican co-host of the “The View” on ABC who has criticized Mr. Trump for years, will host the convention’s prime-time events on Tuesday, according to the Democratic National Convention Committee.

And Rich Logis, a former pro-Trump pundit, will address the convention in a taped speech on Monday night, according to the Harris campaign. More Republican speakers will be announced on Tuesday, according to the convention committee.

Geoff Duncan, a Republican who was the lieutenant governor of Georgia when Mr. Trump sought to overturn the 2020 election result there, said in a phone call on Monday that he would also be in Chicago for the convention, but declined to say if he would deliver an address.

Mr. Logis, a co-chairman of Republicans for Harris in Florida, volunteered for Mr. Trump’s 2016 campaign. But he said he ultimately broke with Mr. Trump over his managing of the Covid-19 pandemic, the Jan. 6 attack and Republicans’ opposition to gun control.

Mr. Logis said in an interview that his high-profile role at the convention showed that Democrats understood “unlikely” alliances were needed for the country to “move on from Trump.”

In his taped speech, he will say, “You don’t need to agree with everything you hear tonight to do what is right,” according to the Harris campaign. “We need to be able to trust our leaders.”

Republicans have played prominent roles at Democratic conventions before, and cross-party endorsements have long been a staple of U.S. politics. But Democrats did not play a highly visible role at the Republican convention last month. (The prominent former Democrat Tulsi Gabbard, a onetime congresswoman from Hawaii, has backed Mr. Trump.)

Democrats have aggressively courted disaffected Republicans since Mr. Trump’s political rise. Two weeks ago, the Harris campaign unveiled its Republicans for Harris program, tapping into an existing network of Republicans who opposed their party’s embrace of Mr. Trump for a third straight presidential campaign. The Harris campaign highlighted endorsements from moderate, anti-Trump Republicans such as former Gov. William F. Weld of Massachusetts.

At the Democratic convention in 2020, former Gov. John R. Kasich, a centrist Ohio Republican, endorsed Joseph R. Biden Jr. in a recorded speech, a move that prompted some hand-wringing from progressives. Mr. Kasich will not attend this year’s convention, his spokesman, Jim Lynch, said.

Democratic leaders seem to have once again judged that the benefits of reaching conservative and centrist voters outweigh the risks of offending some on the left — but the convention will also include left-wing voices, including Representative Alexandria Ocasio-Cortez of New York, who will have a high-profile speaking slot this year after receiving only a brief opportunity to address the convention in 2020.

The Trump campaign, which did not immediately reply to a request for comment on the presence of Republicans at the Democratic convention, separately issued a statement on Monday saying that voters “should look to AOC’s speech tonight for a sense of what Kamala Harris would do with four more years in office.”