The queen spent four days lying in state at the Palace of Westminster to allow members of the public to pay their respects. Her coffin was moved to the abbey early Monday for the state funeral service, which is scheduled to begin at 6 a.m. ET.
London’s Metropolitan Police service said it was engaged in its largest policing operation ever.
Biden arrived separately from many of the dignitaries, accompanied by first lady Jill Biden.
Members of royal families across Europe confirmed that they were attending, including Spain's King Felipe VI and Queen Letizia, and the previous Spanish king and queen, Juan Carlos and Sofia. Denmark's Queen Margrethe II and her heir, Crown Prince Frederik, were also attending.
Royal households from Norway, Sweden, the Netherlands and Belgium all confirmed that they were traveling to London for the funeral, according to Reuters. Monarchs attending from outside Europe include Japan's Emperor Naruhito and Empress Masako.
Other high-profile leaders from Europe who are attending, as reported by Reuters, are German President Frank-Walter Steinmeier, Italian President Sergio Mattarella and Irish President Michael D. Higgins.
Senior officials from the Commonwealth have also confirmed that they are attending, including New Zealand Prime Minister Jacinda Ardern, Australian Prime Minister Anthony Albanese, Canadian Prime Minister Justin Trudeau and Indian President Droupadi Murmu.
Chinese Vice President Wang Qishan was expected to attend the funeral, angering some British lawmakers who were banned from traveling to China last year, after they criticized Beijing's mistreatment of Muslim Uyghurs. China has denied any abuse of the Uyghurs. On Sunday, House of Commons Speaker Sir Lindsay Hoyle said Chinese officials had been barred from visiting the Westminster Hall for the queen’s lying in state.
Invitations to the funeral were sent to heads of state of nearly every country in the world except Syria, Venezuela, Afghanistan, Russia, Belarus and Myanmar.
Britain does not have full diplomatic ties with Syria, Venezuela or Afghanistan, and relations with Russia and Belarus collapsed after Moscow invaded Ukraine in February. Russia's military has used Belarus as a base to launch attacks into Ukraine.
And the U.K. has reduced its diplomatic presence in Myanmar after a military coup there last year.