The country crooner looked well in a dark T-shirt, jeans and jacket along with grey beanie.
Hill addressed the crowd to inform them about her husband's condition.
"When a spotlight was switched on him, he was slumped on his knees on the lefthand side of the stage", Del Crooks, a member of the audience, tells the BBC. "I apologize, but I made the decision that he can not come back out onstage".
A rep for McGraw later confirmed he had received medical attention on-site and would be fine.
The three-day C2C: Country to Country festival saw McGraw and other stars including Kacey Musgraves, Sugarland, Little Big Town and Kelsea Ballerini perform over the course of three days in London, Glasgow and Dublin.More news: National Geographic magazine owns up to 'racist' past
The gig, at Dublin's 3 Arena was the final date of a three-day, three-city tour of the United Kingdom, as part of the Country to Country festival.
The country music superstars were the headliners on the opening night of Country To Country music festival at London's O2 arena.
Following a break of about 20 minutes, Hill came to the front of the stage, flanked by her and McGraw's band members, and explained that McGraw would not be coming back out - a decision made by Hill.
The duo is scheduled to begin their 29-city Soul2Soul tour in the US on May 31 in Richmond, Virginia.
Recently, McGraw made headlines as being one of the few mainstream country artists to voice support for gun control. While fans cheered as Tim McGraw took to the stage and showcased his stellar voice, the awe soon turned into worry when the 50-year-old passed out after performing his song "Humble & Kind."