Like his half-brother, Julian Lennon, Sean has pursued a career in music. His initial efforts were collaborations. He appeared on Lenny Kravitz's 1991 album Mama Said, formed backing-band IMA for his mother's 1995 album Rising, and has collaborated with the New York-based Japanese duo Cibo Matto.
In 1999, he made a guest appearance on the underground hip-hop collaboration, Deltron 3030, working with genre legends Del the Funky Homosapien and Dan the Automator. Oddly enough, Sean's role in the song seems to be what the realistic hell that Earth has become, antithetical to his father's song, "Imagine." His lyrics in the song are this:
"Looking up the sky is red, cities burning overhead. We can make the best of it, in this post-apocolypse."
Through his association with Cibo Matto, he was approached by the Beastie Boys' Adam Yauch, who expressed an interest in Sean's music. His debut solo album, Into the Sun, was released in 1998 on the Beastie Boys's record label, Grand Royal Records. It garnered positive reviews. Regarding Grand Royal, Sean has said, "I think I found the only label on the planet who doesn't care who my parents are and what my name is. It's a good feeling to know that I wouldn't have gotten the offer if they wouldn't have liked my songs. That's pretty rare in the music business!"