Republican Senator Susan Collins says she will vote to confirm Brett Kavanaugh's Supreme Court nomination.
The move all but ensures that the Senate will elevate the conservative judge to the nation's highest court, despite allegations that he sexually assaulted women decades ago.
The dramatic Senate floor announcement by the chamber's most moderate Republican ended most of the suspense over a battle that had left Mr Kavanaugh's fate in doubt for nearly a month after the first accusation against him.
It all but assured a victory for President Donald Trump's quest to move the Supreme Court to the right, perhaps for decades, and a satisfying win for Senate Majority Leader Mitch McConnell.
The Senate's showdown roll call confirmation vote is expected on Saturday afternoon.
With Republicans controlling the chamber by a narrow 51-49, Ms Collins' "yes" vote essentially assured a minimum of 50 votes for Mr Kavanaugh.
Republican Lisa Murkowski of Alaska, a fellow moderate and friend of Ms Collins, has indicated that she will vote no, calling Mr Kavanaugh "a good man" but maybe "not the right man for the court at this time".
Vice President Mike Pence planned to be available on Saturday in case his tie-breaking vote was needed.
Mr Kavanaugh's path to the court seemed straightforward until mid-September, when Christine Blasey Ford accused him of drunkenly sexually assaulting her in a locked bedroom at a 1982 high school gathering.
Two other women later emerged with sexual misconduct allegations from the 1980s, all of which Mr Kavanaugh has denied.