UFC Freedom 250 took place on the White House South Lawn to mark three occasions at once: the 250th anniversary of American independence, Flag Day and Trump's birthday.
The US leader, a longtime MMA fan, walked out from the White House to the arena alongside UFC president Dana White, a close personal friend.
Twelve jets flew over the Washington at the start of the show.
The event featured seven bouts, with Georgian-Spanish fighter Ilia Topuria facing American Justin Gaethje in the main fight.
Polish President Karol Nawrocki was among the guests invited to the event, joining over 4,000 attendees on the White House grounds, including First Lady Melania Trump, politicians, lobbyists and business figures such as Meta CEO Mark Zuckerberg.
A large portion of the crowd was military personnel.
An additional 85,000 to 100,000 fans watched on screens set up in nearby Ellipse Park.
Reactions among those present were enthusiastic.
"I think the president can do whatever he wants. It's his house," one spectator told the Polish news agency PAP.
Another, Taylor from South Carolina, called it "a once-in-a-lifetime event."
Not everyone's a fan
Public opinion more broadly appears less supportive.
A Reuters/Ipsos poll found only 16 percent of Americans considered the White House venue appropriate, with 46 percent opposed.
Even among Republicans, just 31 percent approved.
Some 18 percent of respondents identified themselves as MMA fans.
After the event, Trump was set to travel to France for the G7 summit.
Earlier on Sunday, he announced a preliminary peace agreement between the US and Iran, and said he had ordered the Strait of Hormuz reopened and the blockade of Iranian ports lifted.
(ał)
Source: PAP