- First film appearance was as an uncredited extra in The Ten Commandments (1956).
- First major film role was in the 1957 western Hell's Crossroads.
- Most famous for playing Napoleon Solo in the 1960s TV series The Man from U.N.C.L.E.
- Even after achieving fame as an actor, he continued his education, earning a Ph.D. in Communications from the University of Southern California in 1970.
- Was involved for many years in political causes; a longtime Democrat, he campaigned for candidates such as John F. and Robert F. Kennedy.
- Was a member of the Vietnam War-era group Another Mother for Peace, as well as Dissenting Democrats.
- Received a star on the Hollywood Walk of Fame in 1998.
- 1978, Emmy — Outstanding Continuing Performance by a Supporting Actor in a Drama Series: Winner
- 1961, Golden Globe — New Star of the Year - Actor: Nominee
- 1959, Oscar — Best Performance by an Actor in a Supporting Role: Nominee
- 1979, Emmy — Outstanding Supporting Actor in a Limited Series or Special: Nominee
- 1966, Golden Globe — Actor in a Television Series: Nominee
- 1965, Golden Globe — Actor in a Television Series: Nominee
- 1960, Golden Globe — Best Performance by an Actor in a Supporting Role in a Motion Picture: Nominee
- 1970, BAFTA Film Awards — Best Supporting Actor: Nominee
- Caitlin Vaughn — Daughter
- Linda Staab — Wife
- John Ladd Connor — Stepfather
- Marcella Gaudel — Mother
- Gerald Walter Vaughn — Father
- Cassidy Vaughn — Son
- Attended University of Minnesota, Minneapolis, MN, United States; attended Los Angeles City College, Los Angeles, CA, United States; Los Angeles State College of Applied Arts and Sciences, Los Angeles, CA, United States (MA in Drama)