Joe Biden said the Queen reminded him of his mother after the monarch hosted him and the First Lady for tea at Windsor Castle.
The US President and First Lady Jill Biden travelled to the Berkshire royal residence on Marine One on Sunday after attending the G7 summit in Cornwall.
Before leaving the UK, Mr Biden, 78, shared details of his conversations with the 95-year-old head of state and revealed he had invited her to visit the White House.
The Bidens landed in the grounds just before 5pm, a few minutes ahead of schedule, and were greeted by the Queen in the castle's quadrangle.
A Guard of Honour gave a royal salute and the US national anthem was played.
Mr Biden accompanied the Officer Commanding the Guard of Honour, Major James Taylor, and Major General Christopher Ghika to inspect the Honour Guard.
He then returned to the platform to watch the military march-past with the Queen and First Lady.
The Bidens walked into the castle with the Queen via the Sovereign's Entrance at 5.18pm.
Mr Biden walked alongside the Queen who said to the president: "You completed your talks."
He replied: "Yes we did."
The Queen introduced the Bidens to her lady-in-waiting Dame Annabel Whitehead.
The palace said the couple spent around 40 minutes inside the castle, with the whole visit lasting more than an hour in total.
The chefs at Windsor Castle have trained in the best restaurants and hotels in the country, and will likely have made classic sandwiches and a range of cakes - with some of the ingredients sourced from royal estates.
The tea in the castle's Oak Room comes after the Bidens met the Queen on Friday when she attended a reception for G7 leaders at the Eden Project.
Following the visit and before his departure from the UK, Mr Biden spoke about the Queen to reporters.
He said they had spoken about Russian president Vladimir Putin and China's leader Xi Jinping.
Mr Biden said: "We had a long talk. She was very generous. I don't think she'd be insulted but she reminded me of my mother.
"In terms of the look of her and just the generosity. She was very gracious."
He added he had invited the monarch to the White House, saying: "She said, 'What's it like in the White House?' I said, 'Well it's magnificent but it's a lot of people'."
The carefully-choreographed arrangements to welcome Mr Biden echo the welcome given to Donald Trump in 2018, when the then-US president travelled to Windsor to meet the monarch.
Mr Biden, who is in the UK for the G7 summit, was the 13th American leader to meet the monarch, with Lyndon B Johnson the only one the Queen has not met.
Her tea with Mr Biden comes the day after the Queen received her official birthday gift from the the armed forces - a ceremony in her honour - which was held at the castle.
The traditional Trooping the Colour ceremony, which is normally staged in London, was ruled out for the second successive year because of the threat of coronavirus.