Joe Biden said the US-UK special relationship is in "real good shape" as he met Rishi Sunak in the White House's Oval Office.
The President told Mr Sunak the US doesn't "have a closer ally than Great Britain" and said he was "delighted" the Prime Minister was in Washington DC.
Mr Sunak thanked President Biden for his "warm words", as he mentioned "the strength of our partnership, our friendship".
"We will put our values front and centre as we've always done," he added.
The two leaders sat down for talks - where they joked and laughed - ahead of a formal press conference later.
President Biden spoke about how Winston Churchill and President Roosevelt met in the same place just over 70 years ago.
"They asserted to the strength of the partnership between Great Britain and the United States with the strength of the free world. I still think there's truth to that assertion," he said.
Mr Sunak joked that he wouldn’t be found wandering the corridors of the White House in the early hours of the morning like Mr Churchill once did.
During his two-day visit to Washington DC, the PM has been staying across the road in Blair House, the President’s Guest House.
The US government purchased the property after Eleanor Roosevelt found Mr Churchill wandering towards the family’s private quarters at 3am, cigar in hand.
Mr Biden said: “There’s an awful lot of stories that are told, probably a bunch apocryphal about former prime ministers.”
The PM chipped in: “Wondering around at 3am in the morning? Winston Churchill bothering Mrs Roosevelt.”
He added: “Sir, don’t worry, you won’t see me there bothering you and the First Lady.”
Mr Biden began the conversation by accidentally referring to the PM as "Mr President".
Correcting himself, he told Mr Sunak: "Mr President? I’m just promoting you, Mr Prime Minister. It’s great to have you back.
“In the past few months we have met each other in San Diego and then we met in Belfast and we met Hiroshima.
“And now we're here we're going solve all the problems of the world in the next 20 minutes."
During the meeting, the President referenced work the nations had worked on including a defence partnership between the US, the UK and Australia, called AUKUS, the Good Friday Agreement, and their work with NATO.
"And together, we're providing economic humanitarian aid and security assistance to Ukraine in their fight against the Russians," he added.
President Biden said he hoped to discuss "plans to further strengthen our economic relationship" during Mr Sunak's visit.
He said he thought the global economy was undergoing "the greatest transformation" since the Industrial Revolution as he said he wanted to discuss artificial intelligence with the PM.
The Prime Minister replied: "It's daunting to think of the conversations that our predecessors had in this room when they had to speak of wars that they fought together, peace won together, incredible change in the lives of our citizens.
"And again, for the first time in over half a century, we face a war on the European continent.
"And as we've done before, the US and the UK, have stood together to support Ukraine and stand up for the values of democracy and freedom and make sure that they prevail, as I know we will.
"But also I completely agree with what you said, our economies are seeing, perhaps the biggest transformation since the Industrial Revolution, as new technologies provide incredible opportunities, but also give our adversaries more tools for harm."
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