Upon leaving Naked Raygun, He formed the band Pegboy with brother Joe Haggerty, Steve Saylors, and Larry Damore.

[1] The eldest son of a plumber father and a librarian mother, Haggerty first picked up the guitar at age 16.

His early influences included Jimmy Page, Ritchie Blackmore, Michael Schenker and Brian Robertson.

John also plays in a band called the Nefarious Fat Cats which features an all star line up including himself and brother Joe, Jake Burns of Stiff Little Fingers, Herb Rosen of Beer Nuts and Rights of the Accused, Mark DeRosa of the band Dummy and Scott Lucas of Local H. John toured with Stiff Little Fingers in mid-2011 as a substitute for Ian McCallum, who could not make the tour due to illness.

[2] In 2021 Haggerty became a member of industrial/punk/hard rock supergroup The Joy Thieves by contributing a guitar track to their song "Nihilist Landscape" from their album, "American Parasite."