Newcombe founded The Brian Jonestown Massacre in San Francisco, California, in 1990. Core members in the early years included Matt Hollywood, Jeffrey Davies, Joel Gion, Travis Threlkel, Peter Hayes (BRMC), Patrick Straczek, Ricky Maymi, Brian Glaze, Elise Dye and Dean Taylor, though the line up was subject to frequent changes. Newcombe wrote the majority of songs, with Hollywood collaborating or contributing others on occasion until his departure in 1998, whereupon Newcombe's name became almost synonymous with the BJM. Newcombe was also heavily involved in the post-production of his albums, often engineering and mixing them on his own. A prolific artist, he authored over 150 songs in a fifteen-year period.
Newcombe founded his own record label which has released albums by The Brian Jonestown Massacre (Bravery, Repetition and Noise and the re-release of Spacegirl and Other Favourites), The Lovetones' (Be What You Want), and Dead Meadow's (Got Live if You Want It). According to the official website, the purpose of the label is to "...release BJM music not available through other channels, and to record new bands which we will be producing from time to time, while pursuing the goal of making the world unsafe for rock and roll". Many of the releases on this label are produced or engineered by Rob Campanella.
Part of his life is featured prominently in the documentary film Dig! which focuses on the tense relationship between The Brian Jonestown Massacre and The Dandy Warhols as both bands struggle for success. Newcombe no longer drinks alcohol, and is married. He lives in Berlin with his wife Katy and their son Wolfgang and actively works on his musical project. His latest works include "Musique de Film Imaginé" released by The Brian Jonestown Massacre in April 2015 and "I Declare Nothing", an album written in collaboration with Canadian singer Tess Parks which saw the light in June 2015.