Former President Donald J. Trump will speak at the conservative event known as CPAC on Feb. 28, his first public appearance and lengthy address since he left the White House for a final time last month.

A senior aide to Mr. Trump confirmed that he would attend the Conservative Public Action Conference, which is being held in Orlando, Fla., this year, and that he planned to talk about the future of the Republican Party as well as President Biden’s immigration policies, which have been aimed at undoing Mr. Trump’s.

What Mr. Trump plans to talk about and what he ultimately says once he’s onstage often diverge, as he discards scripts that aides prepare for him.

But it will be the first time that he has spoken in a public setting since the deadly Jan. 6 riot by his supporters at the Capitol building.

The former president, who was permanently banned from Twitter and who is facing investigations into his businesses as well as whether he has culpability for the assault on the Capitol, has generally kept a low profile, except for giving a small round of interviews to sympathetic news outlets about the death of the radio host Rush Limbaugh last week. Even though the interviews were supposed to be about Mr. Limbaugh, Mr. Trump still strayed into repeating his false claims that the 2020 election was stolen from him.

But CPAC is traditionally a cattle call for Republican candidates for office as well as aspiring figures in the party. And Mr. Trump has signaled to several allies and advisers in recent days that he is focused on running for president again in 2024.

Whether he actually does is an open question. But his presence could freeze the field for the next two years, preventing other candidates from developing operations and, more important, networks of donors to sustain their candidacies.

Mr. Trump is currently locked in a battle with Senate Minority Leader Mitch McConnell, Republican of Kentucky, over the party’s future and what kind of candidates it attracts. Mr. McConnell has made it clear that he wants to try to minimize Mr. Trump’s influence after the deadly riot.

But Mr. Trump has said he will try to encourage candidates who will carry his brand of politics forward.

The CPAC conference is the event where, a year ago, when it was held in Washington, D.C., Mr. Trump gave a speech downplaying the threat of the novel coronavirus and insisting that his administration had the situation in hand. A New Jersey man who attended the conference tested positive for the virus, setting off a scramble by officials with the American Conservative Union, who run the conference.

Within two weeks of Mr. Trump’s speech, the pandemic was a full-blown crisis, one that ultimately engulfed his administration. The administration’s failed response to the virus was a key issue for voters in the 2020 election.

Mr. Trump’s modern political life began with a speech at CPAC in 2011.