The US President could be seen arriving at the world-famous abbey as the congregation took their seats for the state funeral service.
Mr Biden left his Beast vehicle and held hands with wife, Jill, as they made their way towards the congregation.
Heads of state and overseas government representatives, including foreign royal families, governors-general and realm prime ministers initially gathered at the Royal Hospital, Chelsea, on Monday morning.
They then travelled under collective arrangements to the venue, now over 1,000 years old.
Mr Biden said he spoke to King Charles III last week, to “offer my condolences on the passing of Queen Elizabeth II”.
He added: “I recalled her kindness, dignity, and constancy – and how she deepened the friendship between our nations.
US President Joe Biden arriving at Westminster Abbey
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Joe and Jill Biden leaving the Beast motorcade
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"I also let the King know that I hope to continue a close relationship with him."
A White House statement added that the 79-year-old “fondly” remembered Queen Elizabeth II's kindness and hospitality when she hosted the Bidens for tea at Windsor Castle after the G7 summit in Cornwall in June last year.
It is believed Queen Elizabeth II's funeral will be the "largest single policing event ever undertaken" in London as mourners and well-wishers from all over the world flock to pay their respects.
The outpouring of grief has not been restricted to those invited to the funeral itself, with thousands lining the streets or taking up spots in one of the city's public parks to get a view of Her Majesty's coffin.
The event on Monday is expected to be bigger even than the policing response around the 2012 Olympics and this year's Platinum Jubilee celebrations.
US President Joe Biden
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King Charles III pays his respects to his late mother during a vigil on Friday evening
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In a security briefing to the media, Deputy Assistant Commissioner Stuart Cundy said “almost every force in the country” had officers involved in the policing operation around the Capital.
The senior commander said some 20,000 officer shifts were being worked throughout the week leading up the funeral.
He said the policing operation would increase significantly as the funeral approaches, but could not give details of the number of officers likely to be involved.
DAC Cundy said the event was a “truly national policing operation, and difficult to compare to any other event".