The US president presented the popular Irishman with the trophy at the west of Ireland course owned by the Trump family on Sunday after Lowry had trounced the field for a remarkable 11-stroke win.
Trump was among the spectators during a 48-hour visit to Ireland. He arrived on Saturday after meeting Irish leaders in Dublin, forcing play to pause while his presidential helicopter landed between a fairway and a nearby field of cows.
Lowry, who described Saturday's interruption as "an insane day", had taken control with an eight-under course record the day before and came one shot from matching it on Sunday, draining an 18th hole birdie to finish with a 23-under-par total.
"He was unbelievable. He's a great guy," Trump said of Lowry, before further delighting the home fans by saying he was going to take tariffs off Irish whiskey.
Lowry, who fought back tears as he paid tribute to his family at the end of his round, thanked Trump and Irish Prime Minister Micheal Martin for being at the event, saying it was amazing to have a US president in attendance.
The 2019 British Open champion's record 11-shot victory came 17 years after he became just the third amateur player to win a European Tour event at his home tournament.
Trump, wearing a suit and white USA cap, greeted Lowry on the first tee and watched from a few feet away as he teed off. Trump told reporters that Lowry was "playing great", with Lowry later laughing at how it had been "a bit mad" to have the President watching on.
While thousands of anti-Trump protesters marched through Dublin on Saturday, the president was cheered heartily throughout Sunday and during a brief appearance in the club bar in the adjoining hotel where he stayed on Saturday night.
Trump watched the action on both days from an 18th-green balcony alongside his sons, Don Jr. and Eric and some of his grandchildren. He was joined by U.S. major champions Brooks Koepka and Patrick Reed, who finished in second place.
Lowry finished on a 257 total, seven shots better than the previous 72-hole record of 264 by Jon Rahm at Lahinch in 2019.
Reed shot 64 and Joaquin Niemann 67 to finish in joint-second place, while the leading Australian was David Micheluzzi, who ended a decent week in style with a last-round 65 that left him tied for 23rd on four-under.
15°C