The US Democrat party won control of the US Senate after Jon Ossoff beat David Perdue in the Georgia runoff.
Ossoff, 33 becomes the youngest person to become a senator in 40 years.
Nancy Pelosi, the House speaker, said in a statement: “Reverend Raphael Warnock and Jon Ossoff ran and won on the values of advancing equality and opportunity for working people across the state and the nation."
With the result in Georgia, the Democrats and the Republicans will now each have 50 seats in the Senate, which is the upper house of Congress.
However, the incoming vice-president, Kamala Harris, will preside over the Senate once she takes office and will have the tie-breaking vote.
This gives the Biden administration a greater chance of achieving its agenda on issues such as healthcare and climate change.
The Senate also has the power to approve or reject Mr Biden's nominees for cabinet and judicial posts.
The results were another nail in the coffin for Donald Trump, who made one of his final trips in office to Georgia to rally his loyal base behind the state’s Republican candidates.
Republicans were considered the favourites heading into Tuesday’s run-offs, given that the party had dominated the political landscape in Georgia for decades. However the Democrats were propelled to victory by Black voters, young voters and new arrivals to a state that is diversifying immensely.
Black voters cast 32% of the ballots, a slight increase from the presidential election two months ago, according to AP VoteCast.
Black voters accounted for about 60% of ballots for Democrats, according to the survey of 3,700 voters in the runoff elections.
The coalition closely mirrored the one that handed Georgia’s electoral college votes to President-elect Joe Biden, the first Democrat to win the state since 1992.
Warnock and Ossoff campaigned on ending the coronavirus crisis in order to reopen the economy. They also pushed for debt-free public college and a new Voting Rights Act.
The Reverend Al Sharpton was among the civil rights leaders who applauded Warnock and Ossoff.
Sharpton, who heads the National Action Network, said in a statement: "Georgia electing its first Black Senator-elect and first Jewish American Senator-elect in our time is a sign of a new America. We are bringing America back to where we ought to be and moving forward towards change."
Warnock and Ossoff were also celebrated beyond Georgia, with supporters from across the US recognising the significance of their win for Black and minority ethnic Americans, and political control in Washington.