Jennings formed Acid Reign in 1985, along with Howard "H" Smith, Kevin "Kev" Papworth, Ian Gangwer and Mark Ramsey Wharton,[9] while attending Harrogate High School (then-called "Granby").[10] After recording their debut EP, Jennings departed from the band in 1988, being replaced by Adam Lehan.[11] Then in 1989, Jennings was contacted by ex-Napalm Death vocalist Lee Dorian with the proposition of forming a band together, which would end up becoming Cathedral, and would also include then-Acid Reign guitarist Adam Lehan.[9] In 1994, Jennings would briefly form a band called Septic Tank with Lee Dorrian, Repulsion vocalist and bassist Scott Carlson and Trouble drummer Barry Stern.[12] Cathedral would announce their breakup shortly after the release of their 2013 album The Last Spire,[13] leading to Jennings reforming Septic Tank, this time with Jaime "Gomez" Arellano, due to Barry Stern's death in 2005.[12] In 2014, Jennings released the self-titled album for a band he formed in 2010 called "Death Penalty".[8] Jennings would also form a band called Lucifer with Andy Prestidge of Angel Witch and Johanna Sadonis, formerly of the Oath; however, Jennings would later depart from the band, being replaced by ex-Entombed drummer Nicke Andersson.[14][15]