Active since the late '80s, he has released over a dozen albums and acquired a cult following among fans of bizarre, offbeat humor. His work has little in common with the shock-jock style of more famous prank callers such as the Jerky Boys or Crank Yankers, instead having a more absurdist bent resembling the radio sketches of Scharpling & Wurster or the awkward anti-comedy of Neil Hamburger. Typical LPC gags include repeatedly calling up businesses asking for nonexistent products, calling strangers and posing empty threats, or pretending to be a UPS employee delivering ridiculous parcels, such as tanks full of insects, and demanding payment. He delivers all of his lines in a deadpan monotone voice, rarely raising his voice, and his skill for quick-witted one-liners and non sequiturs is without parallel. More often than not, the individuals on the other end of the receiver are confused and/or enraged, although on occasion they seem amused, and in later years, some recognize that it is Longmont Potion Castle calling them. On earlier recordings, sometimes LPC edits out his own voice, leaving only the retorts of the callers reacting to his absurd demands or statements.

LPC is a highly skilled musician and recording studio engineer, and he includes thrash metal instrumentals and sample-based collages in his albums. He also uses a Digitech RDS 8000 digital delay unit to alter his voice during his calls, adding to the surrealist nature and confusing his subjects even more. His recordings have been sampled by numerous rock, electronic, and experimental artists, including the Orb, Doormouse, Tit Wrench, and the Amino Acids. Tobacco, leader of electronic psych-pop group Black Moth Super Rainbow, is a devoted fan, and has included LPC tracks in his DJ mixes; LPC has also remixed Black Moth's song "Windshield Smasher." LPC also contributed guitar to a song on Electric Six's 2007 album I Shall Exterminate Everything Around Me That Restricts Me from Being the Master.

As a bored, restless teenager, Longmont Potion Castle began recording prank phone calls on his mother's answering machine during the '80s. His first cassette appeared in 1988, and was billed as a compilation of recordings found in a dumpster. A second volume followed in 1992, and a third appeared in 1995. All of these were 90-minute cassettes issued via the artist's own D.U. Records, and primarily available through direct mail order. They attracted a fan base through word of mouth, and Vinyl Communications, a California-based noise label home to early releases by Kid606 and Lesser, issued two Best of Longmont Potion Castle CDs. Vol. 4 (with cover art paying tribute to Black Sabbath's similarly titled fourth album) was released on CD by Post Replica in 2002, and Late-Eighties-Vein (a rare non-numerically titled LPC album) appeared on Insides Music in 2003.

In 2004, LPC began reissuing his older albums on CD-R, slightly editing them down from the original cassettes. He also released a split 7" single with Hatebeak, a grindcore band fronted by a parrot. Reptilian Records issued the single in 2004, followed by Vol. 5 in 2005. In 2006, LPC performed a few solo thrash metal concerts, and Longbox Option Package, a limited box set containing all of LPC's albums as well as a bonus disc of metal interludes and a DVD, was released. At the time, he announced it as his final release, but Vol. 6 appeared in 2008.

Since then, a new LPC album has appeared on a nearly annual basis, usually available as a CD-R or digital download with bonus tracks. 9 was issued as a double LP in 2012, and included one of his more infamous pieces, a call to the Clown Motel in Tonopah, Nevada. In late 2015, D.U. Records released a split double LP containing an album by Seattle-based instrumental rock group the Albert Lerner Trio, as well as LPC's remix of the album. Later in the year, another limited LPC box set was issued, containing every prior release with bonus material, two DVDs, and a shirt. Around this time, LPC gave several high-profile interviews with publications such as Rolling Stone, Vice, and The A.V. Club, and announced 13 for an early 2017 release. It was also announced that a Longmont Potion Castle documentary titled Where in the Hell Is the Lavender House? was in the works. ~ Paul Simpson