The son of character actor Ed Begley, Sr., he began acting while still a teenager, appearing on the TV series My Three Sons when he was 17. Begley performed as a stand-up comic at colleges and nightclubs and worked briefly as a TV cameraman before landing a string of guest appearances on TV series such as Happy Days and Columbo. He debuted onscreen in Now You See Him, Now You Don't (1972), going on to play small roles in a number of minor films; by the mid '70s he was getting somewhat better roles in better films. Begley became well-known in the '80s, portraying Dr. Erlich on the TV series St. Elsewhere; for his work he received an Emmy nomination. His success on TV led to much better film roles, but he has never broken through as a big-screen star.