The state visit, by far the most high-profile and consequential of Charles' reign, marks the 250th anniversary of the US declaration of independence from British rule, and is the first to the country by a United Kingdom monarch for two decades.
Charles and Camilla touched down at Joint Base Andrews about 2.30pm ET and will head to the White House for a private meeting with self-proclaimed royal fan President Donald Trump.
The King and Queen disembarked from their plane together and were greeted at the foot of the aircraft by US chief of protocol Monica Crowley and the UK ambassador to the US Christian Turner.
Camilla walked down the steps of the plane with a brooch pinned to her chest featuring the US stars and stripes crossed with the Union flag.
The royal couple stood side by side as a band performed the UK and US national anthems, before they got into a vehicle.
The week's schedule includes an address to Congress, a lavish state dinner at the White House and a stop in New York City.
The long-planned visit has become enmeshed in a political spat between the two countries' governments over the US-Israeli war on Iran, which led Trump to voice deep displeasure with UK authorities for failing to support the offensive.
The shooting on Saturday at the White House Correspondents' Association dinner in Washington DC, where US officials have said the president and members of his administration were the likely targets, has cast a further pall over the visit.
Buckingham Palace said the trip would still go ahead as planned following discussions between UK and US authorities to determine if the incident would affect the royals' plans.
"The King and Queen are most grateful to all those who have worked at pace to ensure this remains the case and are looking forward to the visit getting underway tomorrow," a palace spokesperson said on Sunday.
On arriving in Washington DC, the King and Queen have a private tea with the president, an unabashed lover of the royal family who regularly describes Charles as a "great man," and his wife first lady Melania Trump.
The 77-year-old monarch, who is still undergoing treatment for cancer, will address Congress the next day - just the second time a UK monarch has done so.
The royals will then head on to New York where they will commemorate those killed in the September 11, 2001 attacks ahead of the 25th anniversary, while the Queen will also mark the centenary of children's stories featuring Winnie the Pooh.
The US trip concludes in Virginia with the King meeting those involved in conservation work, a nod to his half-century of environmental campaigning.
The government of UK Prime Minister Keir Starmer is hoping the visit will shore up the future of the two allies' "special relationship" which is at its lowest point since the Suez Crisis in 1956.
UK ambassador to the US Christian Turner said the visit would underscore the shared history, sacrifice and common values between the two countries, adding that the approach would be a very British one: "Keep calm, carry on."
with PA
