The 95-year-old British monarch greeted the Bidens in the Quadrangle of the castle, home to the royal family for nearly 1,000 years and where she has spent much of her time since the outbreak of the coronavirus pandemic.
The queen has already met the Bidens on their visit to Britain, having hosted a reception for the leaders of the Groups of Seven rich nations and their spouses on Friday night in Cornwall, on the southwest tip of England where a three-day summit has been held.
Biden is the fourth president and first lady she has received at Windsor, following the Trumps in 2018, the Obamas in 2016, President George W. Bush and his wife in 2008 and the Reagans in 1982.
During her 69 years on the British throne, the longest reign of any English monarch, there have been 14 U.S. presidents, of which Elizabeth has met all except for Lyndon Johnson.
After leaving Windsor, Biden will head off to a NATO summit in Brussels on Monday, a U.S.-EU summit on Tuesday and a meeting with Russian President Vladimir Putin in Geneva the following day.