Trump, who never conceded the November 3 election, did not mention Biden by name in his final remarks as president on Wednesday morning, when he touted his administration's record and promised to be back “in some form”. He boarded Air Force One for the last time and headed to his Mar-a-Lago retreat in Florida.
Top Republicans, including vice-president Mike Pence and the party's congressional leaders, attended Biden's inauguration, along with former US Presidents Barack Obama, George W. Bush and Bill Clinton.
Biden's running mate, Kamala Harris, the daughter of immigrants from Jamaica and India, became the first Black person, first woman and first Asian American to serve as vice-president after she was sworn in by US Supreme Court Justice Sonia Sotomayor, the court's first Latina member.
Harris used two Bibles, including one owned by Thurgood Marshall, the first Black US. Supreme Court Justice.
Biden takes office at a time of deep national unease, with the country facing what his advisers have described as four compounding crises: the pandemic, the economic downtown, climate change and racial inequality. He has promised immediate action, including a raft of executive orders on his first day in office.