Sitting alone watching the parade, the 95-year-old Queen chose a pale grey outfit with yellow detail by her dresser Angela Kelly. The three then went inside for tea.
Biden also told reporters it's important for China to be more transparent so the world knows where the virus came from, including if it was "an experiment gone awry in a laboratory".
In 2008, when then USA president George W Bush met with the monarch at Windsor, he enjoyed a traditional English afternoon spread of tea, small sandwiches and cakes in the White Drawing Room.
The visit comes after a hard year for the monarch and just three days after what would have been her husband's 100th birthday. President Biden has cited his mother Catherine, who died in 2010 at the age of 92, as the "profound influence" on his life, helping him to overcome a stutter in his youth and organising the coffee morning fundraisers when he first ran for the Senate in 1972 at the age of 29.
The Democrat and his wife Jill arrived five minutes after the Queen got there with Prince Charles and the Duke and the Duchess of Cambridge.
Britain's royal family have had a turbulent year in the public eye following a bombshell interview given by the queen's grandson Prince Harry and his wife, Meghan, the Duchess of Sussex.
The Queen and the first lady waited as the president inspected the Guard of Honour.
During her 69 years on the British throne, the longest reign of any English monarch, there have been 14 US presidents, of which Elizabeth has met all bar Lyndon Johnson.
In that time, President Biden inspected the guard of honour whilst Her Majesty and Dr Biden watched on. The firing of a 41 gun salute from Windsor Castle's East Lawn also marked the occasion. Though Biden, unlike Trump, opposed Brexit and is committed to transatlantic relations, his Irish roots - and outspoken support for upholding the Good Friday Agreement - could lend a degree of awkwardness to the meeting.
That same day, Jill Biden joined Kate on a visit to a local school and led a roundtable discussion on the importance of early childhood on lifelong outcomes. The first lady wore a baby blue blazer and skirt.
"She was very generous", Biden said.
He said she reminded him of his mother in the "look of her and her generosity".
During her 69 years on the throne, there have been 14 United States presidents. "I hope that will be soon". When he was a senator, Biden traveled to the U.K.in November 1982 for a meeting of the British-American Parliamentary Group and participated in an audience with Queen Elizabeth II.
"No I didn't. We've been busy.
She wanted to know what the two leaders that I - the one I'm about to meet with, Mr Putin, and she wanted to know about Xi Jinping, and we had a long talk".