Moments after Ms Collins pledged to back Mr Kavanaugh, Democratic Senator Joe Manchin, in a tough race for re-election in West Virginia where Mr Trump is popular, also declared his support, leaving little doubt of a Republican victory.
The only party dissenters were Republican Senator Lisa Murkowski, who had meant to vote no, and Democrat Joe Manchin, who voted yes.
He said events had "strained out basic principles of fairness and justice" and that the vote showed the Senate was "an institution where evidence and facts matter". Collins told reporters she would announce later how she would go.
Senate Democratic Leader Chuck Schumer said Mr Kavanaugh represents "a hard-right, conservative jurisprudence, far, far away from what average Americans believe".
On Friday, both Collins and Murkowski delivered lengthy floor speeches explaining their reasoning behind their votes. The pair will not change the outcome of the vote.
All four lawmakers who'd been undeclared said little or nothing to reporters as they left the chamber.
Lisa Murkowski "will never recover" from the political consequences of opposing now-confirmed Brett Kavanaugh's nomination to the Supreme Court, The Washington Post reported.
There's no guarantee that the senators who supported moving forward will back Kavanaugh on the final vote.
He said Democrats' treatment of Kavanaugh has been "nothing short of monstrous".
"Confirming Brett Kavanaugh in the face of credible allegations of sexual assault that were not thoroughly investigated, and his belligerent, partisan performance.undermines the legitimacy of the Supreme Court".
After less than a week of investigation, the FBI presented its 1,000-page document, in which Republicans said it told them "nothing new" about the allegations, and did not corroborate Ford's story. Democrats belittled the bureau's findings, saying agents constrained by the White House hadn't reached out to numerous other people with potentially important information.
Hundreds of protesters against Mr Kavanaugh assembled on the grounds of the Capitol and at the Supreme Court earlier today.
With approximately 300 opinions issued in 12 years as a judge and a raft of legal articles and speaking engagements, Kavanaugh was the most prolific of the nominees Trump was said to be considering for the role.
Democratic leader Chuck Schumer of NY looked ahead to November, appealing to voters beyond the Senate chamber: "Change must come from where change in America always begins: the ballot box". That reflected Democrats' lasting umbrage over Republicans' 2016 refusal to even consider Merrick Garland, President Barack Obama's nominee to replace the late Antonin Scalia.
Christine Blasey Ford testifies to the Senate Judiciary Committee on Capitol Hill in Washington, on September 27, 2018. And it was fought against the backdrop of the #MeToo movement and Trump's unyielding support of his nominee and occasional mocking of Kavanaugh's accusers.
Yet Kavanaugh's pathway to confirmation seemed unfettered until Ford accused him of drunkenly sexually assaulting her in a locked bedroom at a 1982 high school gathering. Two other women also came forward with sexual misconduct allegations against Kavanaugh. Kavanaugh denies the accusation.
Two women have now accused Mr Kavanaugh of sexual assault when he younger.
"She's instilled in me a commitment to public service and a respect for the rule of law that I've tried to follow throughout my career", Kavanaugh said at his 2006 Senate confirmation hearing for a spot on the U.S. Court of Appeals for the District of Columbia Circuit.
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