The new president declared that democracy had prevailed as he pledged to defend the constitution, while urging Americans to overcome their differences in the search for unity.
At Mr Biden's side was his vice-president Kamala Harris, the first woman, the first Black American, and first person of South Asian descent to hold the nation's second highest office.
Conspicuous by his absence was the outgoing president Donald Trump, who had flown to Florida earlier in the day, while promising his fans to be "back in some form".
Mr Biden has promised that tackling the coronavirus pandemic will be top of his agenda.
