Dillman played Painter Richard Pickman in the TV adaptation of H.P. Lovecraft's 1926 story, "Pickman's Model", presented as the opening act of a December 1971 Night Gallery episode.

Bradford Dillman was born on April 14, 1930 in San Francisco, California, the son of Josephine (née Moore) and Dean Dillman, a stockbroker. Bradford’s paternal grandparents were Charles Francis Dillman and Stella Borland Dean. He studied at Town School for Boys and St. Ignatius High School. He later attended the Hotchkiss School in Connecticut, where he became involved in school theatre productions. While at Yale, he enlisted in the U.S. Naval Reserve in 1948. He graduated from Yale University in 1951 with a BA in English Literature. While a student, he was a member of the Yale Dramat, Fence Club, Torch Honor Society, The Society of Orpheus and Bacchus, WYBC and Berzelius.

After graduation, he entered the United States Marine Corps as an officer candidate, training at Parris Island. He was commissioned as a second lieutenant in the Marine Corps in September 1951. As he was preparing to deploy to Korea, his orders were changed, and he spent the rest of his time in the Marine Corps, 1951 to 1953, teaching communication in the Instructors' Orientation Course. He was discharged in 1953 at the rank of first lieutenant.

Studying with the Actors Studio, he spent several seasons apprenticing with the Sharon, Connecticut Playhouse before making his professional acting debut in The Scarecrow in 1953.

Dillman took his initial Broadway bow in the Eugene O'Neill play Long Day's Journey Into Night in 1956, playing the author's alter ego character Edmund Tyrone and winning a Theatre World Award in the process. The production also featured Frederic March, Florence Eldridge and Jason Robards Jr., and ran for 390 performances until 1958.

In 1957, Katharine Cornell cast him in a Hallmark Hall of Fame television production of Robert E. Sherwood's Pulitzer Prize winning 1940 play, There Shall Be No Night.

Dillman was cast in the melodrama A Certain Smile (1958), for which he earned a Golden Globe award. He followed this with In Love and War (1958), a wartime melodrama starring many of 20th Century Fox's young contract players. It was a box office success. So too was Compulsion (1959), starring Dillman, Dean Stockwell and Orson Welles for Producer Richard Zanuck and Director Richard Fleischer.

Dillman shared a Best Actor award with co-stars Stockwell and Welles at the Cannes Film Festival. After making A Circle of Deception (1960) in London, Dillman was reunited with Welles, Fleischer and Zanuck for Crack in the Mirror (1960), shot in Paris. It was a flop. Back in Hollywood, Fox cast Dillman in support of Yves Montand and Lee Remick in Sanctuary (1961). They also put him in the title role in Francis of Assisi (1961).

From 1956–62, Dillman was married to Frieda Harding, and had two children (Jeffrey and Pamela) with her. He met Actress and model Suzy Parker during the filming of A Circle of Deception (1960). The couple married on April 20, 1963, and had three children, Dinah, Charles, and Christopher. The marriage lasted until Parker died on May 3, 2003.

When he left Fox, Dillman mostly concentrated on television. He co-starred with Barbara Barrie on The Alfred Hitchcock Hour in the episode "Isabel" (1964) and with Peter Graves in Court Martial (1966). He guest-starred on series such as Ironside, Shane, The Name of the Game, Columbo, Wild Wild West, The Eleventh Hour, Wagon Train, The Greatest Show on Earth, Breaking Point, Mission Impossible, The Mary Tyler Moore Show, Barnaby Jones and Three for the Road, and a two part episode of The Man From U.N.C.L.E., which was made into the feature film The Helicopter Spies (1968).

Dillman appeared twice on the Western television series, The Big Valley (1965–69), once in Season 2, episode 15, entitled Day of the Comet, airing on December 26, 1966, and the second time in Season 3, episode 9 appearing in the episode entitled A Noose is Waiting, which aired on November 13, 1967. He appeared in occasional films during this period such as A Rage to Live (1965), Sergeant Ryker (1968), and The Bridge at Remagen (1969).

Dillman appeared in made-for-TV movies such as Fear No Evil (1969), Moon of the Wolf (1972), and Deliver Us from Evil (1973). His film work included Escape from the Planet of the Apes (1971), The Way We Were (1973), Gold (1974), Bug (1975), The Enforcer (1976), The Swarm (1978), Piranha (1978), Sudden Impact (1983), and Lords of the Deep (1989). His last known acting appearance was on an episode of Murder, She Wrote in 1995, a series in which he made eight guest appearances.

Dillman's football fan book, Inside the New York Giants, was published in 1995. An autobiography, Are You Anybody?: An Actor's Life, followed in 1997.

Dillman lived for many years in Montecito, California, and helped raise money for medical research. He died in Santa Barbara, California on January 16, 2018, aged 87, from complications of pneumonia.