Democrats have secured an outright majority in the US Senate with Raphael Warnock's victory in Georgia, in a major gain for Joe Biden's party.
Mr Warnock defeated Herschel Walker, the Republican candidate backed by Donald Trump, in a runoff election on Tuesday night.
Mr Warnock, 53, the incumbent senator and a longtime pastor at Martin Luther King's former church, won 50.8 per cent of the vote.
Mr Walker, 60, a former American football star and businessman, won 49.2 per cent.
"The people have spoken," Mr Warnock told supporters as he thanked them in his victory speech on Tuesday night.
The result bolsters Democrats' position in the upper chamber of Congress, giving them a 51-49 majority for the remainder of Mr Biden's term.
Just called @SenatorWarnock to congratulate him on his win.
Tonight Georgia voters stood up for our democracy, rejected Ultra MAGAism, and most importantly: sent a good man back to the Senate. Here’s to six more years. pic.twitter.com/ibx5aprVs3
— President Biden (@POTUS) December 7, 2022
The party had already seized control of the chamber, since Kamala Harris, the Vice-President, has the ability to cast tie-breaking votes.
But the additional seat grants Democrats greater control of Senate committees, speeding up confirmation of Mr Biden's judicial nominees and other appointees.
It also curbs the power of any individual Democratic senator to stall Mr Biden's legislative agenda, as the centrist West Virginia senator Joe Manchin has done on multiple occasions.
Ms Harris congratulated Mr Warnock on Tuesday night. "Georgia voters said they wanted a Senator who would fight for them — and made it a reality when they reelected @ReverendWarnock to the U.S. Senate. Congratulations, my friend," she wrote on Twitter.
The runoff was called after neither Mr Warnock, nor Mr Walker, received 50 per cent of the vote on November 8.
The historic race, between two black candidates, became one of the most closely watched and costly of the midterm cycle. An estimated $400 million was spent on the race.
Mr Walker conceded on Tuesday night, telling supporters: “There’s no excuses in life and I’m not going to make any excuses now. We put up one heck of a fight".
His defeat caps off an abysmal performance for Mr Trump's endorsed candidates, calling into question his self-proclaimed status as his party's kingmaker.
The former president's candidates for senate and governor were defeated in a number of critical states, including Arizona and Pennsylvania.
Meanwhile the victory by Mr Warnock, Georgia's first black senator, appears to confirm the shifting political landscape in the deep south.
The once ruby-red state flipped blue in the 2020 presidential election for the first time since Bill Clinton's win in 1992.
Tuesday night's result appears to have confirmed Georgia's status as a critical battleground state, following on from two 2021 Senate runoffs that handed Democrats control of the Senate in the last Congress.
Mr Warnock's victory was powered by African American voters, roughly a third of Georgia's electorate, and an increasingly decisive voting bloc within the state.
Mr Warnock, who framed his campaign within the legacy of Dr King's civil rights activism, made a nod to his historic election in his victory speech.
He becomes the first black senator to win a full, six-year term in the state, having previously won a special election in January 2021.
“I am Georgia,” Mr Warnock said in his victory speech. “I am an example and an iteration of its history, of its pain and its promise.”