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.

He started in the 80’s recording with a band called Homeland. Besides his own group, Newcombe has worked with a number of bands, most notably The Dandy Warhols, The High Dials, The Manvils, Innaway, and The Quarter After. He recorded and produced Dead Meadow’s album Got Live if You Want It, and has recorded a cover of Ewan MacColl’s song ‘Dirty Old Town’ with Lorraine Leckie on her 2008 album Four Cold Angels.

In 2016 he composed the soundtrack for British indie film Moon Dogs, directed by Philip John.