0223 GMT February 17, 2019
Kavanaugh was sworn in shortly after the Senate voted 50-48 in his favor – a move that cemented the high court's shift to the right under the Republican leader, who has chosen two of the nine sitting justices, AFP reported.
Protesters rallied in Washington and other US cities against the ascent of the 53-year-old judge, who has faced multiple allegations of sexual misconduct and been criticized for his angry partisan rhetoric.
The two-vote margin of victory made it the closest Supreme Court confirmation vote since 1881 – and by far the most contentious since Clarence Thomas in 1991.
"This is a historic night," President Donald Trump told supporters at a rally in Kansas after signing Kavanaugh's commission aboard Air Force One.
Trump will host Kavanaugh at the White House for a public swearing-in ceremony on Monday, following Saturday's formal oath-taking at the high court.
Kavanaugh's nomination as a replacement for retiring justice Anthony Kennedy was controversial from the start – but the initial focus was solely on his conservative views. But his ascent to the Supreme Court was thrown into doubt when university research psychologist Christine Blasey Ford testified that he had sexually assaulted her at a party when they were in high school.
Ahead of the Senate vote, protesters vented their rage on the steps of the US Capitol.
As they chanted "Shame!" and "November is coming!" police took several dozen demonstrators down the steps and put them in plastic flex-cuffs.
Later, the protesters moved to the Supreme Court, at one point rushing the steps and banging on the building's ornate bronze doors.
"I am here because President Trump mocked sexual assault victims," said North Carolina native Kara Harrington, 50.
In the Senate chamber, the vote was disrupted on several occasions by angry protests from the gallery.
Republican Senate Majority Leader Mitch McConnell, who has railed against Kavanaugh's critics, said he was "proud" of his colleagues and predicted a bright future for his party.
Indeed, Kavanaugh's confirmation reflects a high-water mark of the Trump presidency, before the halfway point: Republican control of the White House, the Senate and the House of Representatives, along with a firm conservative majority on the judiciary's top court.
But the saga – fueled by ugly accusations and counter-claims aired at nationally televised hearings, followed by an 11th-hour FBI probe to address the assault allegations – has inflamed political passions.
The nomination laid bare the partisan gridlock on Capitol Hill and the political polarization of America, ahead of the midterm Congressional elections set for November 6.
In Kansas, Trump seized on the moment to skewer his opponents.
"The radical Democrats have turned into an angry mob," he said.
He hailed Kavanaugh as "a man of great character and intellect".
Democratic senators, who worked to block Kavanaugh, insisted the caustic battle would motivate their party faithful at the polls next month.
"It is a sad day, but the recourse will have to be on election day," Democratic Senator Amy Klobuchar told reporters.
Senator Lisa Murkowski, the only Republican to oppose Kavanaugh, said it was time for the Senate – and Americans – to "heal" after such a divisive few weeks.