Dellums attended Oakland Technical High School and McClymonds High School. He served in the United States Marine Corps from 1954 to 1956. Dellums later received his A.A. degree from the Oakland City College, now Merritt College in 1958, his B.A. from San Francisco State University in 1960, and his M.S.W. from the University of California, Berkeley in 1962. He became a psychiatric social worker and political activist in the African-American community beginning in the 1960s. He also taught at San Francisco State University and the University of California, Berkeley.