The Celebrity star performed his new single Today for the newlyweds' first dance at their reception in Nolensville, Tennessee.
Farr tells People.com his bride suggested he write a song for the big day, but he couldn't come up with anything on the spot - and then tour mate Brad showed him a clip of the video for his new single, and the singer knew that was the song he wanted to dance to after exchanging vows with Hannah Freeman.
"I've written a ton of songs about her but she wanted one for our wedding," Farr says. "My buddy Lee Brice wrote I Don't Dance for his own wedding - the perfect wedding first dance song - and I could not live up to that expectation.
"I was on his (Paisley) bus and he showed me the video and I just teared up. I'm very blunt and I was like, 'That song was amazing and I want to surprise my fiancee with something really special. Would you come and play this song for our first dance?'"
Paisley jumped at the chance to perform the song at the wedding, allowing Farr to pull off a wedding day surprise.
"She had no idea," he adds. "It was so cool of Brad to take the time to do that. He's a good friend and a great guy."