Horan, 27, and Anne-Marie, 30, performed their duet "Our Song" during Monday's episode of the NBC late-night show.
Horan and Anne-Marie gave an atmospheric performance alongside the vintage car that appears in their "Our Song" music video.
Anne-Marie shared behind-the-scenes photos from the Tonight Show on Instagram.
"Only a few hours to go until me and @niallhoran's #OURSONG performance on @falltonight I'm SO EXCITED!!!!" she captioned the post.
Horan and Anne-Marie released the "Our Song" music video in May. In the video, Horan and Anne-Marie play jewel thieves on the run.
"Our Song" appears on Anne-Marie's forthcoming second studio album, Therapy, set for release July 23.
"It's full of happy, sad, revenge, love and revelation and I hope you feel all of those things when you listen to it," Anne-Marie said on Instagram in May.
Anne-Marie released her debut studio album, Speak Your Mind, in 2018. Horan, a member of the former boy band One Direction, released his second solo album, Heartbreak Weather, in March 2020.