Mr Biden said on Thursday that Ms Harris had run an “inspiring” campaign and praised her “great” character.
“She gave her whole heart effort, and she and her entire team should be proud of the campaign they ran,” he said.
“You know, the struggle for the soul of America since our very founding has always been an ongoing debate and still vital today.
“I know for some people, it’s a time for victory — to state the obvious. For others, it’s a time of loss. Campaigns are contests of competing visions. The country chooses one or the other. We accept the choice the country made.”
‘We are not defeated’
Mr Biden echoed Ms Harris’s message that she had conceded the election but not “the fight that fuelled this campaign”.
He said: “Remember, a defeat does not mean we are defeated. We lost this battle. The America of your dreams is calling for you to get back up.”
Mr Biden is likely to pass a number of executive orders in the coming months before he leaves office. He is reportedly considering a massive package of military aid for Kyiv, using leftover funds already authorised by Congress.
He could also take executive action to give environmental protection to areas where Mr Trump is planning to drill for oil. The Republican has promised to “drill baby, drill” from the first day of his administration and reduce federal support for green energy.
Mr Biden is the oldest president to leave office, but no longer the oldest person to win office. At 78, Mr Trump is older than the Democrat was when he won the 2020 election.
Mr Trump is also the first president with federal criminal convictions to win a presidential election. Several further ongoing cases against him are now unlikely to proceed.