WASHINGTON — The Senate confirmed Pete Hegseth as the nation’s defense secretary late Friday in a dramatic tie-breaking vote, swatting back questions about his qualifications to lead the Pentagon amid allegations of heavy drinking and aggressive behavior toward women.

Rarely has a Cabinet nominee faced such wide-ranging concerns about his experience and behavior as Mr. Hegseth, particularly for such a high-profile role atop the American military. But the Republican-led Senate was determined to confirm Mr. Hegseth, a former Fox News host and combat veteran who has vowed to bring a “warrior culture,” rounding out President Trump’s top national security Cabinet officials.

Vice President Vance arrived to break the 50-50 tie, highly unusual for Cabinet nominees and particularly defense secretaries, who typically win wider bipartisan support. Mr. Hegseth himself was at the Capitol with his family.

“We have a great secretary of defense and we’re very happy,” Mr. Trump said as he boarded Air Force One after surveying fire devastation in California.

Mr. Trump said he didn’t care about the dissent from Senator McConnell, the influential former Republican leader — who joined two other Republicans, Senator Murkowski of Alaska and Senator Collins of Maine, in voting against Mr. Hegseth — because the “important thing is winning.”

The Senate’s ability to confirm Mr. Hegseth despite allegations against him provides a measure of Mr. Trump’s political power and ability to get what he wants from the GOP-led Congress to complete his agenda at the White House.

Only once before has the vice president had to break a tie on a Cabinet nominee — during Mr. Trump’s first term, when Vice President Pence cast the vote to confirm Betsy DeVos as education secretary.

Next week senators will be facing Mr. Trump’s other outside Cabinet choices including particularly Kash Patel as the FBI director; Tulsi Gabbard as director of the office of national intelligence; and Robert F. Kennedy Jr., an anti-vaccine advocate, at Health and Human Services.

“Is Pete Hegseth truly the best we have to offer?” said Senator Reed of Rhode Island, the top Democrat on the Senate Armed Services Committee, urging his colleagues to think seriously about their vote. All Democrats opposed the nominee.

But Senate Majority Leader Thune said Mr. Hegseth, as a veteran of the Army National Guard who served tours in Iraq and Afghanistan, “will bring a warrior’s perspective” to the top military job.

“Gone will be the days of woke distractions,” Mr. Thune said, referring to the diversity, equity and inclusion initiatives being slashed across the federal government. “The Pentagon’s focus will be on war fighting.”

Mr. Hegseth himself was working the phones late Friday to shore up his support, his confirmation at stake.

“He’s a good man,” Mr. Trump said of Mr. Hegseth while departing the White House to visit disaster-hit North Carolina and Los Angeles. “I hope he makes it.”

The uncertainty sent tensions soaring late Friday at the Capitol. It takes a simple majority to confirm nominees, and Republicans, with a 53-47 majority in the Senate, could only lose one more objection after Ms. Murkowski and Ms. Collins already announced they would vote no.

Mr. McConnell had signaled skepticism in an earlier speech when he declared he would confirm nominees to senior national security roles “whose record and experience will make them immediate assets, not liabilities.”

One Republican, Senator Tillis of North Carolina, sent the Senate swirling as he raised fresh questions and was provided information and answers.

But Mr. Tillis ultimately voted to confirm Mr. Hegseth, who he said “has a unique perspective” and is passionate about modernizing the military. He said he spoke to Mr. Hegseth for “nearly two hours” about his concerns.

In contrast, Mr. McConnell said after the vote said Mr. Hegseth “did not reckon” with the reality of job, noting that the nominee’s “mere desire to be a ‘change agent’ is not enough.”

Democrats, as the minority party, have helped confirm Secretary of State Marco Rubio and CIA Director Ratcliffe in bipartisan votes to Trump’s national security team.

A Princeton and Harvard graduate, Mr. Hegseth represents a newer generation of veterans who came of age in the aftermath of the Sept. 11, 2001, attacks. He went on to a career at Fox News as the host of a weekend show, and was unknown to many on Capitol Hill until Trump tapped him for the top Defense job.