"Forgot how good this song is," the Canadian singer-songwriter wrote on TikTok.
The vocalist was accompanied only by an acoustic guitar for the stripped-back performance.
The two stars recorded the duet as part of their Niall Horan's Homecoming: The Road to Mullingar With Lewis Capaldi film.
"Stupid Love" was the lead single off Gaga's 2020 album, 'Chromatica.'
