President-elect Joe Biden is poised to nominate retired four-star army general Lloyd J Austin to be secretary of defence, making him the first black leader of the Pentagon.

Sources say Mr Biden has selected Gen Austin over long-time front-running candidate Michele Flournoy, a former senior Pentagon official and Biden supporter who would have been the first woman to serve in the role.

Mr Biden had also considered Jeh Johnson, a former Pentagon general counsel and former secretary of homeland defence.

It is understood Mr Biden offered and Gen Austin accepted the post on Sunday.

As a career military officer, the 67-year-old Gen Austin is likely to face opposition from some in Congress and in the defence establishment who believe in drawing a clear line between civilian and military leadership of the Pentagon.

Although many previous defence secretaries have served briefly in the military, only two — George C Marshall and James Mattis — have been career officers. Gen Marshall also served as secretary of state.

Like Gen Mattis, Gen Austin would need to obtain a congressional waiver to serve as defence secretary. Congress intended civilian control of the military when it created the position of secretary of defence in 1947 and prohibited a recently retired military officer from holding the position.

One of the people who confirmed the pick to The Associated Press said Gen Austin’s selection was about choosing the best possible person, but acknowledged pressure had built to name a candidate of colour and that Gen Austin’s stock had risen in recent days.

Mr Biden has known Gen Austin at least since the general’s years leading US and coalition troops in Iraq while Mr Biden was vice president. Gen Austin was commander in Baghdad of the Multinational Corps-Iraq in 2008 when Barack Obama was elected president, and returned to lead US troops from 2010 through 2011.

Gen Austin also served in 2012 as the first black vice chief of staff of the army, the service’s No 2-ranking position. A year later he assumed command of US Central Command, where he fashioned and began implementing a US military strategy for rolling back the so-called Islamic State militants in Iraq and Syria.

Gen Austin retired from the army in 2016, and thus would need a congressional waiver of the legal requirement that a former member of the military be out of uniform at least seven years before serving as secretary of defence. That waiver has been granted only twice — most recently in the case of Gen Mattis, the retired marines general who served as Donald Trump’s first Pentagon chief, but resigned in 2018 in protest at the president’s policies.

Loren DeJonge Schulman, who spent 10 years in senior staff positions at the Pentagon and the National Security Council, said she understood why Mr Biden would seek candidates with a deep understanding of the military. However, she worries that appointing a general to a political role could prolong some of the damage caused by Mr Trump’s politicisation of the military.

“But retired generals are not one-for-one substitutes of civilian leaders,” she said. “General officers bring different skills and different perspectives, and great generals do not universally make good appointees.”

Gen Austin has a reputation for strong leadership, integrity and a sharp intellect. He would not be a prototypical defence secretary, not just because of his 41-year military career but also because he has shied from the public eye.

He earned the admiration of the Obama administration for his work in Iraq and at Central Command, although he disagreed with President Obama’s decision to pull out of Iraq entirely in December 2011.

Gen Austin was involved in the Iraq War from start to finish. He served as an assistant commander of the 3rd Infantry Division during the invasion of Iraq in March 2003 and oversaw the withdrawal in 2011. When Gen Austin retired in 2016, Mr Obama praised his “character and competence”, as well as his judgment and leadership.

One person familiar with the matter said Mr Biden was drawn to Gen Austin’s oversight of the Iraq pull-out, especially given the military’s imminent role in supporting the distribution of the coronavirus vaccines.

Civil rights leaders have pushed the president-elect to pick more black cabinet members.

The Reverend Al Sharpton said of Gen Austin on Monday: “It’s a good choice that I think many in the civil rights community would support. It’s the first time we have seen a person of colour in that position. That means something, in a global view, especially after such an antagonistic relationship we had with the previous administration.”