President-elect Joe Biden has selected Retired Gen. Lloyd Austin to serve as secretary of defense, according to three people with knowledge of the decision. If confirmed, Austin would be the first Black person to lead the Pentagon.

In picking Austin, Biden has chosen a barrier-breaking former four-star officer who was the first Black general to command an Army division in combat and the first to oversee an entire theater of operations. Austin’s announcement could come as soon as Tuesday morning, people familiar with the plans said Monday.

Austin, who also ran U.S. Central Command before retiring in 2016, emerged as a top-tier candidate in recent days after initially being viewed as a longshot for the job. Michèle Flournoy, Obama’s former Pentagon policy chief, was initially viewed as the frontrunner, but her name was notably absent from Biden’s rollout of key members of his national security team two weeks ago.

Biden had been under growing pressure to nominate a Black person to be his defense secretary in recent weeks. He chose Austin after also considering former Homeland Security Secretary Jeh Johnson for the job, several people familiar with the discussions said.

Lingering concerns about Johnson's tenure in the Obama administration improved Austin's standing among Congressional Black Caucus members in recent days, according to two people, including a House Democratic aide. Johnson has been criticized for his record on expanding family detention and accelerating deportations, as well as approving hundreds of drone strikes against suspected terrorists that killed civilians.

"General Austin is a southerner, has impeccable credentials given his military career and would be an outstanding secretary for the department,” Rep. Bennie Thompson (D-Miss.), a CBC member who is close to Biden, told POLITICO earlier Monday.

A person familiar with Biden’s decision said the president-elect chose Austin because he is crisis-tested and respected across the military. Biden also trusts Austin, as they worked together when Biden served as vice president and had a large foreign policy portfolio.

The president-elect was also drawn to the history-making aspect of Austin’s nomination and his deep logistics experience, which will prove critical as the military helps distribute coronavirus vaccines, the person said.

Biden offered Austin the job Sunday, and he accepted the same day, the person added.

Austin declined to comment through a spokesperson. A spokesperson for the Biden transition team also declined to comment.

Biden and Austin got to know each other during the Obama administration’s Iraq drawdown, when the former vice president led Iraq policy and Austin served as the last commanding general of U.S. forces in Iraq. In that position, Austin played a key role in the surge of forces that began in 2007 and was in charge of the withdrawal of U.S. combat forces in 2011.

Austin’s nomination may run into trouble on Capitol Hill. Austin has not been out of the military for the required seven years and would need a waiver from Congress to become secretary of Defense — and lawmakers have signaled their wariness of granting yet another exception for a retired general to lead the Pentagon just four years after President Donald Trump sought one for his first defense secretary, Jim Mattis.

Austin’s candidacy has also been met with resistance from some national security experts, who expressed concern about the balance of civil-military power in the Pentagon under yet another retired general.

“From a civil-military relations perspective, this seems like a terrible idea,” tweeted Rosa Brooks, a Georgetown University professor and former Pentagon official who wrote an op-ed in The New York Times calling for a woman to be chosen as Defense secretary. “Lots of damage during the Trump era. Especially after Mattis, Kelly, McMaster, Flynn.... putting a recently retired 4 star, no matter how wonderful, into the top civilian DoD position sends the worst possible message.”

Another knock against Austin is that he doesn't have the same star power as Mattis or the other four-star officers of that period. "He just doesn’t knock your socks off,” said a former defense official close to the transition. “I just don’t see him as an independent thinker.”

However, the Biden team saw Austin as the safe choice, said one former defense official close to the transition, adding that the retired general is believed to be a good soldier who would carry out the president-elect’s agenda.

"There would be less tension” with Austin as defense secretary instead of Johnson or Flournoy, the person said. “Maybe less disagreement … the relationship would be smoother.”

CBC Chair Rep. Karen Bass (D-Calif.) on Sunday told CNN that her caucus was backing both Austin and Johnson for Defense secretary, noting that a special CBC task force has been meeting weekly with the Biden-Harris transition team.

But the position wasn't unanimous among the CBC members.

Rep. Anthony Brown of Maryland, the only CBC member on the Armed Services Committee, and Rep. Marc Veasey of Texas backed Flournoy in a letter to Biden last week.

The pair praised her experience in the Clinton and Obama administrations, which they said is needed to retrain the military on matching gains by China and reorienting U.S. counterterrorism policies for a new era, and praised Flournoy as "a tireless advocate for diversity and inclusion in national security."

And on Monday, House Armed Services Chair Adam Smith (D-Wash.) came out in support of Flournoy.

"I've certainly communicated to the Biden people that I think Michèle Flournoy is hands down the best qualified person for the job. That does not mean that she's the only person who can do the job ... but I think Michèle Flournoy is uniquely qualified.”

During his decades of service, Austin earned a reputation for avoiding the limelight and rarely took part in public events such as press conferences or think tank discussions.

In addition to the other firsts, he was also the first Black vice chief of staff of the Army, the service’s second ranking officer.

In 2013, President Barack Obama named him to run Central Command, responsible for all U.S. military operations in the Middle East, where he oversaw operations against the Islamic State when it took over large swaths of Iraq and Syria in 2014.

He faced particularly tough questions in 2015 about the U.S. military’s role training forces in Syria to fight the Islamic State during the country’s civil war, acknowledging that the U.S. spent some $500 million but trained only a handful of fighters.

Another cloud hanging over the command at the time was allegations that Central Command downplayed intelligence reports on the threat posed by the terrorist group and painted a brighter picture of the progress of U.S. military efforts.

Austin’s command was cleared in an investigation by the Defense Department’s inspector general in 2017.

He retired after 41 years in 2016 and joined the board of directors of Raytheon Technologies, one of the largest Pentagon contractors and a potential sticking point among progressive lawmakers, who have raised concerns over appointing a Defense secretary who has ties with industry. He is also on the board of Nucor, the largest American steel producer, as well as health care company Tenet. He is a trustee of the Carnegie Corporation of New York, a philanthropic foundation.

Public records show that he has his own consulting firm, Austin Strategy Group, LLC in Great Falls, Va.