The Prime Minister was greeted at the entrance of 1600 Pennsylvania Avenue by President Trump, before the two leaders disappeared inside for what is expected to be an hour-and-a-half of private discussions.
The pair are likely to discuss the prospect of a US-UK trade deal once Britain leaves the EU and will then hold a joint press conference before enjoying lunch together.
Mrs May and President Trump posed for photographs in the Oval Office, where President Trump showed the Prime Minister the bust of Winston Churchill now that it has been returned to the official office of the presidency.
President Trump said: "This is the original folks, this is the original in many ways and it's a great honour to have Winston Churchill back."
President Trump's predecessor Barack Obama had removed the bust from the room during his eight-year term in office.
Mrs May thanked President Trump, adding: "We're very pleased."
The issue of the bust sparked a diplomatic row during the EU referendum campaign after Vote Leave figurehead Boris Johnson used President Obama's removal of the sculpture as an example of a suggested 'anti-British' attitude.
President Trump shows off the returned Winston Churchill bust to the PM
AFP • GETTY
President Trump greets Theresa May at the White House
AFP • GETTY
May was greeted at the entrance of 1600 Pennsylvania Avenue by President Trump
Mrs May earlier visited the Arlington National Cemetery in Virginia ahead of her meeting with President Trump.
The Prime Minister laid a wreath at the Tomb of the Unknowns, which holds the remains of unidentified US troops from the First and Second World Wars, as well as the Korean conflict, before the Last Post was played.
Arlington, across the Potomac River from Washington D.C., is home to approximately 400,000 graves of fallen US servicemen.
Dressed in sombre black, Mrs May was greeted by troops representing all military units based in Washington, led by Major General Bradley Becker, commander of Joint Force Headquarters for the national capital region.
A cannon was fired 19 times as the Prime Minister's convoy arrived at the cemetery and made its way to the memorial.
AFP • GETTY
Theresa May and Donald Trump will hold a joint press conference together
The Prime Minister will visit President Trump later
May meets Trump: Historic first meeting in pictures
Fri, January 27, 2017
The two leaders will spend about an hour in face-to-face talks in the Oval Office, where President Trump has restored a bust of Winston Churchill removed by predecessor Barack Obama.
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President Trump Meets With British PM Theresa May At The White House
Theresa May will travel to the White House to become the first foreign leader to meet President Trump
President Trump and vice-President Mike Pence laid wreaths at the cemetery last week at the start of their inauguration events.
Former Ukip leader Nigel Farage also recently laid a wreath at the grave of one of a number of British soldiers to be buried at Arlington.
The cemetery is also home to a memorial to the victims of the Lockerbie terror attack and the grave of assassinated US president John F Kennedy.
Last night, the Prime Minister hailed the "unique and special relationship" between Britain and the US in a speech to a Republican Party conference in Philadelphia.