WASHINGTON — President-elect Joseph R. Biden Jr. will formally announce key members of his White House staff on Tuesday, naming Representative Cedric L. Richmond of Louisiana to oversee public outreach and installing Jennifer O’Malley Dillon, who managed his presidential campaign, as a deputy chief of staff, a person familiar with the transition said.

Mr. Biden will also announce that Steve Ricchetti, a longtime confidant, will serve in the White House as a counselor to the president. All three will most likely have offices down the hall from the Oval Office, making them among the most senior aides in the West Wing.

Mr. Richmond will inherit a job once held by Valerie Jarrett in the Obama administration. Kellyanne Conway was President Trump’s counselor, the job that Mr. Ricchetti will take. And Ms. O’Malley Dillon will probably oversee White House operations for Mr. Biden.

A spokesman for the transition declined to comment. A person familiar with the transition planning said the three appointments would be announced along with other members of the president-elect’s staff.

Decisions about cabinet secretaries remain several weeks away, according to people close to Mr. Biden, who has spent several days during the past week in closed-door discussions with advisers about the challenge of winning confirmation fights if the Senate remains in Republican control next year.

By contrast, White House staff positions do not require Senate confirmation, leaving the president-elect wide latitude in selecting his West Wing advisers.

The announcements come as Mr. Biden moves quickly to establish his governing agenda and the team he will need to put it into effect once he takes office. The president-elect is under pressure to fill those jobs with people of diverse ethnic and ideological backgrounds, making good on promises he made during his campaign.

But the appointments of Mr. Richmond, Ms. O’Malley Dillon and Mr. Ricchetti — all loyal lieutenants to Mr. Biden — suggest the importance that he is also placing on surrounding himself with people whose advice he implicitly trusts.

Mr. Richmond, who served as a national co-chairman of Mr. Biden’s campaign and was an early supporter, had been widely expected to join the Biden White House. He brings with him deep relationships across Capitol Hill. His new job was reported earlier by Bloomberg.

Mr. Richmond, a Democrat whose district includes most of New Orleans, has scheduled a news conference for Tuesday where he is expected to announce he is leaving Congress. In a brief phone call on Monday night, he laughingly declined to confirm that he was joining Mr. Biden’s staff but acknowledged that he would discuss his “future” on Tuesday.

Mr. Richmond was formerly the chairman of the Congressional Black Caucus, and he has a close relationship with Representative James E. Clyburn, Democrat of South Carolina, whose endorsement in February helped revive Mr. Biden’s campaign. Mr. Richmond’s district is safely Democratic, and his departure from Congress is unlikely to cost the party another seat after an election where their majority was weakened.

Mr. Richmond is likely to have broad responsibilities in his senior role and will continue to interact with Congress, according to people familiar with the transition. Others said they expected him to serve as one of the people most willing to give the new president frank and candid advice behind closed doors.

Ms. O’Malley Dillon, a veteran of former President Barack Obama’s campaigns, has been credited with steering Mr. Biden’s presidential bid through the difficulties of the coronavirus pandemic and the challenge of running against an unpredictable rival like Mr. Trump. Her appointment was reported earlier by NBC News.

She assumed the role of campaign manager in mid-March, just as the severity of the coronavirus outbreak was becoming clear to many Americans. Two days after she was named to the role, Biden campaign offices around the country shut down. She learned to remotely navigate the team factions and transformed a shoestring primary operation into a general election organization.

Ms. O’Malley Dillon’s team faced criticism and second-guessing over the light footprint Mr. Biden’s campaign maintained in key battleground states during the pandemic, and throughout the campaign there were tensions between some of the earliest Biden aides and those she brought in as she built the team.

But she was respected inside the campaign for streamlining and organizing what had been a small and underfunded operation, and her expected appointment is a clear sign of the degree to which she is trusted by the president-elect.

Mr. Ricchetti is a close adviser and longtime lobbyist who has been by Mr. Biden’s side for years. He lobbied for the pharmaceutical industry and served as Mr. Biden’s chief of staff when he was the vice president.

As one of Mr. Biden’s most trusted advisers and a longtime member of his tight-knit inner circle, Mr. Ricchetti is expected to have a broad portfolio and a senior role within the administration. During the campaign, he maintained deep relationships across Capitol Hill and in the donor community, sometimes serving as a kind of gatekeeper to the campaign for Democratic heavyweights.

Mr. Biden is likely to move quickly on other key White House jobs as well.

He still has to assemble a communications team, including a press secretary, who will often serve as the public face of the administration. Among the possible candidates for that job is Symone Sanders, who has served as one of his top communications advisers during the campaign.

The president-elect will also have to choose a White House counsel, a key job in an era of divided government, when members of the other party often engage in legal clashes with the president. Dana Remus, who worked in the counsel’s office during Mr. Obama’s tenure, was the chief lawyer for Mr. Biden’s campaign.

And Mr. Biden will need to choose aides to oversee national security, homeland security and economics in his White House. Announcements on some of those positions could also come as soon as Tuesday.

Pranshu Verma and Nicholas Fandos contributed reporting.