The monarch and his wife Queen Camilla head across the Atlantic on April 27, a four-day trip ostensibly to mark the 250th anniversary of US independence from Britain but one that now has far greater significance amid a growing spat between Trump and British Prime Minister Keir Starmer.
"The visit ... recognises the challenges the United Kingdom, the United States, and our allies face across the world," a Buckingham Palace spokesperson said on Tuesday.
"This visit is a moment to reaffirm and renew our bilateral ties as we address those challenges together, in the UK's national interest."
Unveiling details of the trip, the spokesperson said Trump and first lady Melania Trump would greet the King and Queen in Washington with a private tea, followed by a ceremonial welcome at the White House, a state dinner, and a meeting between the monarch and president.
As previously announced, the King will also address Congress, becoming just the second British monarch to do so following Queen Elizabeth in 1991.
The royal couple will later visit New York where they will meet families of victims of the September 11, 2001, attacks.
The US leg of their tour ends with a visit to Virginia, before Charles heads off to Bermuda, a British overseas territory where he is the head of state.
Amid the pomp of a royal state visit, the British government hopes the trip will demonstrate the value of what a foreign office spokesperson called "the closest of friendships".
Since the US and Israel launched their attack on Iran, Trump has dismissed Starmer as "not Winston Churchill" and Britain's aircraft carriers as "toys", although the president's affection for Charles and the British royals has remained unwavering.
Opinion polls show Trump is deeply unpopular in Britain, and some politicians have said the visit should be called off.
"(Trump) is a dangerous and corrupt gangster, and that is how we must treat him," Ed Davey, leader of the Liberal Democrat party, said in parliament on Monday.
"I really fear for what Trump might say or do while our King is forced to stand by his side. We cannot put His Majesty in that position."
One issue neither Trump nor the King will want to overshadow the visit is discussion about Jeffrey Epstein.
Some US lawmakers have said the King should meet with Epstein's victims, but a palace source said this would not be possible because it might impact on potential criminal action.
"We fully understand and appreciate the survivors' position," the source said.
"Even though the risk may be small that a meeting or any public comments could impact on those inquiries, or the proper course of the law, that is a risk that we simply can't take, for the best interest for the survivors themselves."
