President-elect Joseph R. Biden Jr is expected to nominate retired General Lloyd J. Austin III, a former commander of the American military effort in Iraq, to be the next secretary of defence, according to two people with knowledge of the selection.

If confirmed by the Senate, General Austin would make history as the first African-American to lead the country’s 1.3 million active-duty troops and the enormous bureaucracy that backs them up.

General Austin, 67, was for years a formidable figure at the Pentagon, and is the only African-American to have headed US Central Command, the military’s marquee combat command, with responsibility for Iraq, Afghanistan, Yemen, Syria — most of the places where the US is at war.

General Austin is known as a battlefield commander. But he is less known for his political instincts — and has sometimes stumbled in congressional hearings, including a session in 2015 when he acknowledged, under testy questioning, that the department’s $500 million programme to raise an army of Syrian fighters had gone nowhere.

He was selected over another front-runner, Michèle A. Flournoy, who had served in senior Pentagon policy jobs and mentored a generation of women in national security who had pushed for her appointment as the first female defence secretary.