Dean established his reputation as a member of the Keith Tippett Sextet from 1968 to 1970, and in the band Soft Machine from 1969 to 1972. Shortly before leaving Soft Machine he started his own group, Just Us. From 1975 to 1978 he led a nine-piece band called Ninesense, performing at the Bracknell Jazz Festival and similar events. His own groups since then, usually quartets or quintets, have most often worked in the free jazz mode, with little or no pre-composed material. At the same time, he continued to work with other groups that are very composition-based, such as guitarist Phil Miller's In Cahoots, drummer Pip Pyle's Equipe Out, and various projects with former Soft Machine bassist Hugh Hopper.
In 2002, Dean and three other former Soft Machine members (Hugh Hopper, drummer John Marshall, and guitarist Allan Holdsworth) toured and recorded under the name Soft Works. With another former Soft Machine member, guitarist John Etheridge, replacing Holdsworth, they subsequently toured and recorded as Soft Machine Legacy, playing some pieces from the original Soft Machine repertoire as well as new works. Featuring Dean, three albums of theirs have been released: Live in Zaandam (CD, rec. 2005/05/10), New Morning - The Paris Concert (DVD, rec. 2005/12/12) and the studio album Soft Machine Legacy (CD, 2006, rec. 2005).
Dean's last musical collaborations also included those with Soft Bounds (a quartet composed of Dean, Hugh Hopper, Sophia Domancich and Simon Goubert) and Alex Maguire's project Psychic Warrior.