The grim milestone came on the same day as global coronavirus cases exceeded 50 million.
Biden's transition website lists four priorities: Covid-19, economic recovery, racial equity and climate change.
President's posts would also no longer be exempt from review by Facebook's fact-checking partners.
British politician whose words he lifted has paid warm tribute to the new US president-elect.
Trump aides and Republican allies, while somewhat conflicted on how to proceed, largely supported his strategy or remained silent.
He becomes the oldest president-elect and brings with him a history-making vice president-elect in Kamala Harris.
Relief was a common theme expressed in many parts of the world to the news that his reelection bid had failed.
The international press also focused on the feat of Kamala Harris, Biden’s running mate who will become the United States’ first female vice president.
Biden’s victory in the battleground state of Pennsylvania put him over the threshold of 270 Electoral College votes he needed to clinch the presidency.