His career next took him to New York, where he worked with artists including Miles Davis, Phineas Newborn, Jr., Billy Taylor, Erroll Garner, Charles Mingus and Sonny Rollins.
He was in a short-lived trio started by Bill Evans, with Jimmy Garrison on bass, in the late 1950s.
Dennis moved to California, when Miles Davis recommended him to Lena Horne.
Recording credits include recordings with such artists as Michel Legrand, Miles Davis, Charlie Mingus, Nancy Wilson, Gerald Wilson and poet Langston Hughes.
Since 1997, Dennis has been an assistant director of the Lab Band at the award-winning Los Angeles County High School for the Arts.