US President Joe Biden celebrated the strengthening of his party's majority in the Senate after Democrat Raphael Warnock was declared the winner of a run-off election in Georgia.
The incumbent senator defeated Republican Herschel Walker, a former football star and protégé of former president Donald Trump, according to projections by television networks.
Mr Warnock's win confirms the very slim Democratic majority - 51 to 49 - in the upper house of Congress.
"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," Mr Biden tweeted.
The party's electoral triumph does not change the balance of power in the Senate, of which Democrats had already secured control on 8 November.
But the win by Mr Warnock, a pastor at the Atlanta church where civil rights leader Martin Luther King Jr once preached, hands Democrats greater control in committees and curbs the power of any individual Democratic senator to sink Biden initiatives.
The Republicans took back the House last month but with a much smaller majority than expected.
Mr Warnock, 53, and Mr Walker, 60, both African American, faced voters after neither earned more than 50% in the 8 November midterm vote.
Democrats retained control of the Senate in that vote with 50 seats, Vice President Kamala Harris's tie-breaking vote giving them the edge in the 100-seat chamber.
Mr Warnock's win significantly curbs the power of centrist Democratic senator Joe Manchin, who has already blocked several major Biden initiatives in the first two years of the president's term.
With 700 days to go before the 2024 presidential election, Republicans hope to stymie Biden's momentum after his party performed much better than expected in November.
Determined to win the race, Democrats called on their top gun: charismatic former president Barack Obama, who campaigned alongside Mr Warnock in Atlanta last week.
And in yet another sign of how high the stakes were, $400 million was spent on the Georgia race to make it the most expensive campaign of the midterms.
Some 1.9 million people voted early, many of them likely Democratic voters, while Republicans were expected to turn out in force yesterday.
Polls had the race too close to call.
Georgia, historically a Republican state, took America by surprise when voters chose Joe Biden over Donald Trump in the 2020 presidential election and then sent two Democrats to the Senate two months later in another run-off.
Both the candidates this time are natives of Georgia but the men are polar opposites.
Mr Warnock grew up in poverty, born the eleventh of 12 children to a former soldier and preacher father and a mother who worked in the cotton fields.
He remained as a senior pastor at Martin Luther King's Ebenezer Baptist Church even after his election and holds a doctorate in theology.
Mr Walker is a latecomer to politics with his 2022 Senate run.
The 60-year-old conservative is considered one of the best players in the history of American college football - a near-religious institution in the south - and went on to have a stellar career in the National Football League.
Mr Walker, who is staunchly anti-abortion even in cases of rape, has been the subject of several recent scandals, having been accused of paying for abortions for two women he had relationships with.