The US president announced the agreement with Tehran just hours before the start of Sunday's Ultimate Fighting Championship event, which was held amid thunderstorm warnings in Washington DC.
Immediately following the card, Trump was due to fly to a meeting of heads from the G7 group of leading democracies in Evian, France, where the settlement reached with Iran to end the four-month-long war was likely to dominate, with full details still to emerge.
The build-up to the cage-fighting event to mark America's 250th anniversary of independence, saw the president and UFC chief Dana White walk together from the Oval Office to the White House balcony overlooking the giant open-sided arena, nicknamed The Claw, on the South Lawn.
The national anthem was then played as a formation of fighter jets streaked overhead, sparking a cheer from the crowd and chants of "USA, USA".
Trump then took his seat close to the signature octagon cage, where the seven fights were to be held.
Among the 4000 guests in the custom-built venue was British heavyweight boxing star, Tyson Fury, wearing a Donald Trump for prime minister baseball hat.
Meta boss Mark Zuckerberg was also spotted speaking to the president during a break in the action.
Others with cage-side seats were FBI director Kash Patel, acting US Attorney-General Todd Blanche and Speaker of the House of Representatives Mike Johnson.
Tens of thousands more watched the Freedom 250 bouts on a big screen in a park close to the White House, with some having travelled from across the country for the spectacle.
It made for some incongruous scenes with fighters pictured warming up inside the formal surroundings of the White House.
While the administration said the UFC would be covering the $US60 million ($A85 million) cost, official documents show seven agencies, including the Department of Homeland Security and the Federal Aviation Administration, had "allocated significant resources and manpower" to the controversial event, which was the subject of an unsuccessful legal challenge.
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