Lawmakers in both parties initially were uneasy at the prospect of granting Mr. Austin a waiver, citing concerns over maintaining civilian control of the military. They had already approved a waiver four years ago for Jim Mattis, President Donald J. Trump’s first defense secretary and a retired four-star Marine officer, and many had vowed then not to do so again.
Civilian control of the military, a political cornerstone of the department since its inception, was strained during the Trump administration with a commander in chief who sought to politicize its role until the very end of his term.
In anticipating the resistance to Mr. Austin and to adjust perceptions about civilian control, the new administration has taken the unusual step of putting a number of political appointees in place before others who require Senate confirmation even get a hearing. Mr. Biden has chosen Kathleen H. Hicks, a Pentagon official under President Barack Obama, to serve in the No. 2 slot, the first woman who would hold that position if confirmed.
“It is clearly a signal that the Biden administration wants the Pentagon to be ready on day one,” Ms. Bensahel said, “and that they want to have as many civilians in place as soon as possible.” The Trump administration left many political slots unfilled for weeks after inauguration.
Facing pressure from Mr. Biden’s transition team and top Democrats, the majority of lawmakers brushed aside their concerns and threw their support behind a barrier-shattering nominee. The vote was the first time since the elder President George Bush that an incoming president has not had a defense secretary installed at the Pentagon on the first day, a distinction that Democratic leaders were acutely aware of as they rushed to tamp down resistance to his confirmation.
“We applaud the Senate’s strong bipartisan confirmation of Lloyd Austin, who has been breaking barriers all of his life, as the first Black secretary of defense in our nation’s history,” said Jen Psaki the White House press secretary. “Secretary Austin’s confirmation is a major benefit to our national security, and he’s going to hit the ground running leading the Pentagon.”
Even though 43 percent of the 1.3 million men and women on active duty in the United States are people of color, the leaders at the top of the military’s chain of command have remained remarkably white and male. When Mr. Obama selected Mr. Austin, then a general, to lead Central Command, he became one of the highest-ranked Black men in the military, second only to Colin L. Powell, who had been chairman of the Joint Chiefs of Staff.