In 1965, soon after discovering the Beatles and turning to rock music, he dropped out of college and moved to Berkeley, California, where he met musicians including Chicken Hirsh and Jerry Garcia. He and Hirsh backed the duo Blackburn & Snow, and Cohen also played boogie-woogie piano in a club, the Jabberwock. There he met guitarist Barry Melton, and was introduced to Country Joe McDonald as a pianist and organistalthough, at the time, Cohen had never played organ. He joined McDonald's new band, Country Joe and the Fish, with Melton, Bruce Barthol, Paul Armstrong and John Francis Gunning later saying: He was a member of Country Joe and the Fish from December 1965 to January 1969, and played on their first two albums, Electric Music for the Mind and Body and I-Feel-Like-I'm-Fixin'-to-Die, as well as several tracks on their third album, Together. Record producer Sam Charters regarded him as "musically more experienced" than the other band members.
Later career
After leaving Country Joe and the Fish, Cohen moved to England before returning to the United States to join the Blues Project in New York in 1971, touring with the band until mid 1972. He has played with many musicians including Janis Joplin, Luther Tucker, Mick Taylor, Tim Hardin, Jimi Hendrix, Johnny Winter, Huey Lewis, Michael Bloomfield and Bob Weir. He also worked as a solo musician, sharing bills with Bonnie Raitt, Richard Thompson, Jerry Garcia, Leo Kottke, Rufus Thomas and others. In 1975, Happy Traum invited Cohen to record instructional lessons on piano for his Homespun Tapes series. Subsequently, he recorded three videotapes on blues piano, audio tapes on blues, rock and ragtime piano, and a separate instructional package on blues piano, David Bennett Cohen Teaches Blues Piano, Volumes I and II. He also recorded two guitar instruction albums for Kicking Mule Records. During the 1990s, he toured with the musicalRent, playing guitar and keyboards. He also recorded with the Bill Perry Blues Band, and toured as part of blues musician Bobby Kyle's band. He released three albums in the 2000s, David Bennett Cohen at the Piano, In the Pocket, and Cookin' With Cohen. He continues to perform in the New York City area, both solo and with the Former Members, a band whose members include Bruce Barthol, Roy Blumenfeld and Greg Douglass. The summer of 2014 saw Cohen tour the UK with San Francisco Nights, including the other Former Members, Sam Andrew and Bex Marshall. Cohen is also a music instructor, and runs workshops. Em 2015 ele participou do Festival de Vinho e Jazz Florianópolis como atração principal com sua banda solo