The US Congress has certified Joe Biden’s victory in the presidential election, hours after Trump supporters stormed the building in an attack that saw four people die.
Lawmakers resumed the session after police managed to remove the mob, which had been encouraged by President Donald Trump in a bid to overturn his defeat.
The certification clears the way for Mr Biden to be sworn in on 20 January.
In response, Mr Trump finally pledged an “orderly transition” of power.
Democrat Joe Biden’s victory was confirmed at about 03:30 local time (08:30 GMT) on Thursday by a joint session presided over by Vice-President Mike Pence, who said the violence had been a “dark day in the history of the United States Capitol”.
Wednesday’s chaotic scenes followed months of escalating rhetoric from Mr Trump and some Republican allies that sought to undermine the result of the 3 November election. The invasion of the Capitol by the president’s supporters – some armed – was an event without precedent in modern American history.
Mr Biden blasted the “insurrection” as Mr Trump, while telling the mob to “go home”, continued to make false claims of electoral fraud. The outgoing president’s Twitter and Facebook accounts were later frozen.
After objections by some Republican lawmakers to overturn the result in Arizona and Pennsylvania were rejected, Congress formally certified the final electoral college vote with Mr Biden receiving 306 votes to Mr Trump’s 232.
Shortly afterwards Mr Trump – whose social media accounts remain blocked – said in a statement: “Even though I totally disagree with the outcome of the election, and the facts bear me out, nevertheless there will be an orderly transition on January 20th.”
Meanwhile, Washington DC Mayor Muriel Bowser said one of the four dead – a woman – was part of a group that forced entry into the House room while it was still in session. They were confronted by plainclothes officers, and an officer pulled out a weapon and fired it.
The woman was taken to hospital and later proclaimed dead. She has not been officially named, but local media identified her as San Diego-area US Air Force veteran and Trump supporter Ashli Babbit.
One woman and two men died as a result of “medical emergencies”, officials said, without giving details. At least 14 members of the police were injured during the unrest.
The rampage came as two Democrats won Senate seats in elections in Georgia, which shifted the balance of Congress to their party’s effective political control. This major political victory will ease the passage of Mr Biden’s agenda after he is inaugurated.
For days Mr Trump had been piling pressure on his vice-president to block certification of the result. But in a letter to Congress on Wednesday, Mr Pence said he had no “unilateral authority to decide which electoral votes should be counted”.
In declaring the final vote totals, Mr Pence said this “shall be deemed a sufficient declaration of the persons elected president and vice-president of the United States.”
Earlier, Senate Republican leader Mitch McConnell also definitively broke with Mr Trump in an emotional speech from the chamber floor, saying: “If this election were overturned by mere allegations from the losing side, our democracy would enter a death spiral.”
After the session resumed, Senate Democratic leader Chuck Schumer blasted the mob at the Capitol as “rioters and insurrectionists, goons and thugs, domestic terrorists”, saying the president “bears a great deal of the blame”.
Senator Kelly Loeffler, who lost her bid for election in Georgia’s vote on Tuesday, said she could no longer in good conscience vote against certification as she had originally planned, citing the “abhorrent” invasion of the Capitol.
With two weeks before Mr Trump leaves office, there are calls for him to be removed beforehand for instigating the attack on Congress. US media say some members of his cabinet have discussed invoking the 25th amendment to the Constitution, dealing with a president deemed unfit for office.
Democrats on the House Judiciary Committee have written saying that Mr Trump’s actions meet the amendment’s requirements.