In 1968, "upon hearing Wendy Carlos' Switched-On Bach", he bought a Moog synthesizer and opened the Different Fur recording studio in San Francisco.
[2] He worked with Herbie Hancock in the early 1970s on two albums (Crossings and Sextant) and subsequent tours, pioneering synthesizers as a live instrument.
[2][3] Hancock initially hired Gleeson as a synthesizer technician and instructor, but ended up asking him to become a full-time band member, expanding the ensemble from six to seven musicians.
Gleeson recorded a number of solo albums, starting with Beyond the Sun - An Electronic Portrait of Holst's "The Planets" in 1976, to which Carlos contributed the sleeve notes.
[6] In 2017 Gleeson retired from film and television scoring and returned to live performance, both as a solo artist and with a trio (Michael Shrieve, drums, and Sam Morrison, reeds).