The Icarus Line was formed in Los Angeles, California in 1998 with Joe Cardamone on vocals, Aaron North on guitar, Lance Arnao on bass and Aaron Austin on drums. After their first tour they added Alvin DeGuzman as a second guitarist. At this time they released their first 7 inch EP Highlypuncturingnoisetestingyourabilitytohate on Hellcat Records. They released the Red and Black Attack EP later that year. Between 1998 and 2000 the band went through 4 different drummers. With their fourth drummer, Mike Felix, the band recorded songs for a split 7 inch with Ink & Dagger, and a single entitled Kill Cupid With a Nailfile for Los Angeles record label Buddyhead records which was (and still is) co-owned by North.
Shortly after, Felix left the band and was replaced by Jeff Watson on drums. In 2000 they recorded their first full-length album, Mono, which was also released on Buddyhead records. Mono was regarded by critics as a fresh take on punk and was influenced by such bands as Born Against and The Jesus Lizard.
The band spent the next two years touring to support the album. By 2003, Watson had exited the band and was replaced by their sixth drummer, Troy Petrey. With this lineup the band recorded a number of songs, including a split release with Burning Brides. Later that year, Watson returned to the band, and Arnao had been kicked out and replaced by Don Devore on bass. Devore was formerly a member of the Philadelphia, Pennsylvania rock/punk band Ink & Dagger which also released some albums on Buddyhead records.