In a speech after the announcement, President-elect Joe Biden said US democracy had been “pushed, tested and threatened and proved to be resilient, true and strong but it’s time to turn the page”.
He condemned President Trump’s attempts to overturn the result and added that the “will of the people prevailed.”
The confirmation was one of the steps required for Mr Biden to take office as it is the norm in America.
Under the US system, voters actually cast their ballots for “electors”, who in turn, formally vote for candidates weeks after the election. Democrat Joe Biden won November’s contest with 306 electoral college votes to Republican Donald Trump’s 232.
President Trump, who shows few signs of conceding, has not commented. Shortly after the electoral college’s vote, he 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 the president’s claims.
Speaking in Delaware, Mr 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.
Solidly Democrat California, with its 55 electors, was one of the last states to vote on Monday and took Mr Biden across the 270-vote threshold required to win the presidency.
The president of the United States is not chosen directly by voters, but by what’s known as the electoral college
Mr Biden described the harassment of officials following the election as “unconscionable” and said: “It’s my sincere hope we never again see anyone subjected to the kind of threats and abuse we saw in this election.”
He also noted that he had the same number of electoral college votes that Mr Trump said was a “landslide” when he won in 2016. Mr Biden emphasized that he had also won the popular vote, something Mr Trump failed to clinch four years ago.
Republican Senator Lamar Alexander said: “The presidential election is over. States have certified the votes. Courts have resolved disputes. The electors have voted. I hope that President Trump will put the country first, take pride in his considerable accomplishments, and help president-elect Biden get off to a good start.”
Electors almost always vote in line with their pledged candidate, although in 2016 some did not and this prompted states to change their laws to try to prevent a recurrence. Analysts say there is next to no chance that Mr Biden’s victory could be overturned.
The number of electors per state is roughly in line with the size of the population.
Donald Trump’s scorched-earth strategy of contesting the results of the 2020 election, however, has given the proceedings new attention.
Although his legal team has had little success in challenging the results of the vote in multiple battleground states, the official recording of the electoral college ballots across the US will effectively lower the curtain on these long-shot judicial manoeuvres.
That does not mean the Trump team is giving up, of course. It is holding alternative electoral college proceedings with an alternate set of votes that will declare the president the real winner. They will continue with futile court challenges and, eventually, ask Congress to overturn the election results.
It is an alternative reality that Donald Trump’s supporters may find more comforting than the one where Joe Biden is president-elect.
Given that the House of Representatives is controlled by Democrats, the official electoral college tally will have been duly certified by the states on Monday and federal law is on Mr Biden’s side. Mr Trump’s chances of success in the real world, however, sit squarely at zero.
The results of the voting process will be sent to Washington DC and formally counted in a joint session of Congress on 6 January presided over by Vice-President Mike Pence. That will pave the way for Joe Biden to be sworn in as president on 20 January.