Biden later pledged to be "a president for all Americans".
ADVERTISEMENTJoe Biden on Wednesday became the 46th president of the United States.
With his wife Jill Biden holding the Bible, Chief Justice John Roberts swore him into office.
At a star-studded ceremony, which saw the Obamas and singer Lady Gaga in attendance, the Democrat pledged to be "a president for all Americans".
You can watch the moment Biden said his oath of office in the video player, above.
Notable by his absence was Donald Trump, who is the first outgoing president not to attend his successor's inauguration in 152 years.
Trump had already departed the White House, staying that it was an "honour" to serve as president and wishing the next administration "great success".
After becoming president, Biden said in his speech that the US must confront the rise of white supremacy and reject manipulated or invented facts.
"The forces that divide us are deep and they are real - but they are not new," he said. "The battle is perennial, and victory is never assured."
"Our better angels have always prevailed," he added, naming moments in US history like the Civil War.
"History, faith and reason show the way of unity."
Those hoping a Biden presidency will spell better relations with the EU would have been pleased to hear him promise to "repair our alliances and engage with the world once again".
Also sworn in at the ceremony was Biden's deputy, Kamala Harris, who became the first woman, as well as the first woman of African American and South Asian descent, to hold the position of US vice president.
The former California senator was sworn in by Sonia Sotomayor, the first Hispanic and Latina member of the Supreme Court.
Biden also referenced the poignancy of Harris' election saying: "Here we stand 108 years ago, thousands of protesters tried to block brave women marching for the right to vote.
"Today we mark the swearing-in of the first woman in American history elected vice-president - Kamala Harris.
"Don’t tell me things can’t change."