Gärdestad was a songwriter who co-wrote lyrics for many of his younger brother Ted Gärdestad's (1956–1997) songs. This included his Melodifestivalen song entries "Oh, vilken härlig dag" in 1973 and "Rockin' 'n' Reelin'" in 1975. As such, Gärdestad also won Melodifestivalen 1979 with Ted's song "Satellit". The song went on to represent Sweden in Eurovision 1979, finishing 17th during the final held in Jerusalem.