He became an assistant at George Martin"s Associated Independent Recording Studios, where he worked on recordings by Roxy Music, Kate Bush, Karlheinz Stockhausen, Jeff Beck and others Cullum worked alongside Geoff Emerick, Steve Nye, Bill Price, Jon Kelly, Peter Henderson, Bob Ezrin, Leiber and Stoller and Chris Thomas. In the 1980s, after touring the world mixing live shows, he formed a production collaboration with Chris Hughes.
Together they worked with Adam and the Ants, Tears for Fears, Wang Chung, Paul McCartney, Ric Ocasek and others
Other artists he has worked with in varying capacities include: Tori Amos, Miguel Bose, Moya Brennan, Enya, Howard Jones, The Human League, The Afro Celt Sound System, Chris Hughes" (Shift - a tribute to Steve Reich), Peter Gabriel, Sa Ding Ding, Robert Plant, MaryJess, Jana Kirschner, Andrew Lloyd Webber, Rufus Wainwright, Mark Ronson, Karen Mok, Zucchero, Don Was and Phildel. Cullum continues to produce, compose, record and mix.
He also currently acts as a consultant in Music Production and A&R, travelling internationally.