Joe Biden’s presidential election victory was confirmed by the US Electoral College.
In a speech after the announcement, the president-elect said US democracy had been “pushed, tested and threatened” and “proved to be resilient, true and strong”.
He condemned President Donald Trump’s attempts to overturn the result.
Later Russian President Vladimir Putin became one of the last world leaders to congratulate Joe Biden on his victory.
Moscow had said it would wait for the official results before doing so. Most other national leaders contacted Joe Biden days after the vote on November 3.
Confirmation by the Electoral College was one of the steps required for Joe Biden to take office.
Democrat Joe Biden won November’s contest with 306 Electoral College votes to Republican Donald Trump’s 232.
Donald Trump, who shows few signs of conceding, has not commented. Shortly after the Electoral College’s vote, the president announced on Twitter the departure of Attorney General William Barr, who had said there was no evidence of widespread voter fraud in the election, despite President Trump’s claims.
Speaking in Delaware, Joe Biden praised “ordinary men and women” who had refused to be bullied, referring to the president’s efforts to question and overturn the results, involving legal challenges which have been rejected by courts across the country.
He described the efforts as “a position so extreme we’ve never seen it before”.
“Respecting the will of the people is at the heart of our democracy, even when we find those results hard to accept,” he said.
“The flame of democracy was lit in this nation a long time ago,” he added.
“And we know that nothing not even a pandemic or an abuse of power can extinguish that flame.”
Joe Biden said it was time to “turn the page, as we’ve done throughout our history, to unite, to heal”.
But he warned that, with the coronavirus pandemic continuing to ravage the US, there would be difficult months ahead.
“There is urgent work in front of us,” Joe Biden said.
“Getting this pandemic under control and getting the nation vaccinated against this virus.”
Joe Biden stressed the importance of immediate economic help that was “so badly needed by so many Americans who are hurting today” and rebuilding the economy to be “better than it ever was”.
He was speaking as the coronavirus death toll in the US rose above 300,000.
Normally the electors do not get that much attention but this year, after uncertainty generated by a raft of challenges to results in Democrat-won states by the Trump campaign, the state-by-state vote was in the spotlight.
Solidly Democrat California, with its 55 electors, was one of the last states to vote on December 14 and took Joe Biden across the 270-vote threshold required to win the presidency.
Heightened security had been put in place in some states, including Michigan and Georgia, ahead of voting, which took place in state capitals and Washington DC.
In Michigan – a key swing state Joe Biden won – legislative offices in the state capital Lansing were closed due to “credible” threats of violence.
The vote at the capitol building went ahead peacefully although a group of Republicans tried to enter the building to hold their own vote and were turned away.