The 50-year-old reportedly stopped the show halfway through, sat down next to the drums to catch his breath and then fell to his knees as he was leaving the stage.
It was McGraw’s wife and singing partner, country star Faith Hill, who came on stage later and explained to the crowd what was happening.
“He’s been super dehydrated, travelling so much. I apologise,” she said.
“But I made the decision that he cannot come back out on stage.”
McGraw’s performance was part of the Country to Country (C2C) music festival, which covers three cities in three days – London, Glasgow and Dublin.
“Tim McGraw was suffering from dehydration in Dublin this evening at the C2C show,” said his representative.
“He was attended to by local medical staff on-site and will be fine. He and Faith thank everyone for their love and support and look forward to seeing their Irish fans again soon.”
The fall took place just as the singer had finished his last hit Humble & Kind.