Supreme Court chief justice John Roberts led Biden in the oath of office, using a Bible that has been in the president’s family since 1893.
His son Beau Biden used the same Bible when he was sworn in as Delaware attorney general in 2007.
In his inaugural address, Biden vowed to “preserve, protect and defend the Constitution of the United States”.
He told the socially distanced crowd: “Through a crucible for the ages, America has been tested anew, and America has risen to the challenge.
“Today we celebrate the triumph not of a candidate but of a cause: the cause of democracy. [...] At this hour, my friends, democracy has prevailed.”
Biden also pledged to heal the rifts that have divided the US over the four years of Trump’s presidency.
He said: “We must end this uncivil war that pits red against blue, rural versus urban, conservative versus liberal. We can do this if we open our souls instead of hardening our hearts.”
Minutes earlier, Kamala Harris had been sworn in as vice president by Supreme Court justice Sonia Sotomayor, the first Latina member of the court. Harris used a Bible that once belonged to Thurgood Marshall, the first Black Supreme Court justice.
Harris’ vice presidency is historic in several regards: she’s the first female, Black and South Asian person to hold the position.
Donald Trump departed the White House shortly after 8am on Wednesday for Joint Andrews Base in Maryland, where he delivered brief unscripted remarks.
“Have a good life,” Trump said during the final moments of his bizarre farewell. “We will see you soon.”
Trump is the first president in 152 years to skip his successor’s inauguration. He still has not formally conceded the election, nor has he reached out to Biden to congratulate him on his victory.
Trump did, however, leave a letter for Biden in the White House, continuing a long-standing tradition between outgoing and incoming presidents.
After a bitter campaign marked by Trump’s baseless allegations of election fraud, Biden struck a conciliatory tone, asking Americans who did not vote for him to give him a chance to be their president as well.
“To overcome these challenges to restore the soul and secure the future of America requires so much more than words. It requires the most elusive of all things in a democracy: unity,” he said.
The ceremony on Wednesday unfolded in front of a heavily fortified US Capitol, where a mob of Trump supporters stormed the building two weeks ago, enraged by his false claims that the election was stolen with millions of fraudulent votes.
The violence prompted the Democratic-controlled House of Representatives to impeach Trump last week for an unprecedented second time.
Thousands of National Guard troops were called into the city after the siege, which left five people dead and briefly forced lawmakers into hiding. Instead of a throng of supporters, the National Mall on Wednesday was covered by nearly 200,000 flags and 56 pillars of light meant to represent people from U.S. states and territories.
“Here we stand, just days after a riotous mob thought they could use violence to silence the will of the people, to stop the work on our democracy, to drive us from this sacred ground,” Biden said. “It did not happen; it will never happen. Not today, not tomorrow, not ever.”