US Supreme Court Chief Justice John Roberts has administered the oath of office to Joe Biden and has taken up the post formally.
Earlier, Kamala Harris, the first black woman vice president of the United States, was also sworn in, making her the first black woman vice president of the United States.
Former presidents Barack Obama, Bill Clinton and George W. Bush are also taking part in the swearing-in ceremony at Capitol Hill.
Outgoing US President Donald Trump, however, left the White House before Biden was sworn in. He is the first US president in 150 years to not attend the inauguration of a new president.
On the other hand, in case of any disturbance, an iron fence was erected around the Capitol Hill building and 25,000 National Guards were deployed.
Corona and 200,000 Americans who were barred from attending the event due to security threats were represented by flags.