While a member of the Asexuals, he fronted the band and helped the Montreal hardcore scene become well known outside the city through the frequent tours the group made in Canada, the United States and Europe.

The band broke up in 1996 and Kastner moved to California; he established himself in Silverlake and started writing music for soundtracks.

with Frank Daly and Mark Arnold of Big Drill Car[4] and released five albums and EPs from 1999 to 2003 before going on a hiatus in 2005.

[5] Kastner wrote music for many movies and TV show soundtracks, including Phil the Alien, Universal Soldier: The Return and Brats of the Lost Nebula.

In 2008, John joined Bran Van 3000 as guitar player and in 2010 reunited with the Asexuals to play a show in Montreal.