Campbell’s film career began in 1950, with a small part in the John Garfield film, The Breaking Point. After several years of similar supporting performances in a number of films, including as a co-pilot in William Wellman’s The High and the Mighty (1954), he won his first starring role in Cell 2455 Death Row (1955), a low-budget prison film for Columbia Pictures. He played a death row inmate, based loosely on the true story of Caryl Chessman, who staunchly proclaimed his innocence and obtained numerous reprieves over many years until finally being executed. Campbell’s surprisingly powerful performance received generally good notices from critics, but it did very little for his career; his next several roles were again providing support to lead actors, including Love Me Tender (1956) (in which he became the first person to sing onscreen with Elvis Presley) and the 1958 film version of Norman Mailer’s The Naked and the Dead.

In 1958, Campbell co-starred with Paul Birch in Cannonball, a short-lived television series about truck drivers. After that, he toiled for more years in small parts in increasingly lower grade movies.  Campbell made two guest appearances on Perry Mason in 1959 and 1960. In his first appearance he played the title character and murder victim Allen Sheridan in “The Case of the Artful Dodger,” then he played murderer and title character Jim Ferris in “The Case of the Ill-Fated Faker.”

In 1963, Campbell began a brief association with Roger Corman, starring in the director’s The Young Racers that year. The auto-racing themed movie, written for the screen by Campbell’s brother Robert Wright Campbell, was shot in Ireland. After production was completed, the film’s sound man, Francis Ford Coppola, talked Corman into allowing Coppola to remain in Ireland with a small crew and direct a low-budget horror film, to be produced by Corman. Coppola promised it would be the cheapest film Corman was ever involved in. Shot for approximately $40,000, the resultant film, Dementia 13 (1963), was an atmospheric and violent horror thriller clearly made in imitation of Psycho. Campbell starred as a moody loner who at one point becomes the chief suspect in a series of gruesome axe killings; Patrick Magee and Luana Anders led the supporting cast. Many years later, Campbell would provide an informative and amusing audio commentary for the film’s DVD release.

Campbell also starred in another, even cheaper and more bizarre, Corman-produced horror yarn. Filmed in 1963 in Yugoslavia under the title Operacija Ticijan, again with Magee in the cast, the movie was never released in its original form, although it was re-edited, re-dubbed and briefly shown on television as Portrait in Terror. Years later, additional footage was shot in California, first by Jack Hill, then by Stephanie Rothman, transforming what was once a spy thriller into the story of a vampire stalking the streets of Venice, California. Retitled Blood Bath, although it also became known as Track of the Vampire, the film received a limited theatrical release in 1966. Campbell’s character was an artist who killed women and hid their bodies in his sculptures; he is also a vampire who can freely walk during the daylight in search of victims. However, the fanged vampire was confusingly played by another actor who did not resemble Campbell. Like Dementia 13, the film has managed to develop a cult following despite its deficiencies. In the early 1990s, Video Watchdog magazine devoted lengthy articles in three separate issues painstakingly detailing the convoluted production history of this strange but fascinating movie.

Campbell has also obtained cult status for his guest starring roles on Star Trek, appearing first as the mischievous super-being Trelane, in an episode of the original series called “The Squire of Gothos”. Campbell also appeared twice as the Klingon Captain Koloth. Campbell first played Koloth on the original Star Trek series in the classic episode “The Trouble With Tribbles.” He reprised the role on the series Star Trek: Deep Space Nine episode entitled “Blood Oath”, some thirty years later. Campbell appeared at several Trek conventions in the 1980s and 1990s and many Star Trek fans consider Campbell’s portrayal of the Trelane character as the first introduction of the “Q culture” to the series. His last appearance was at the convention organized by Creation Entertainment at the Las Vegas Hilton in August 2006.

Campbell was married three times. His first marriage was to Judith Exner in 1952. They divorced in 1958. Exner, at some point, became involved with U.S. President John F. Kennedy. His second wife was Barbara Bricker. They were married from 1960-1961. He married his third wife, Tereza, in 1962 (although some accounts have them marrying in 1963). They were married until his death. He died quietly on April 28, 2011, at the Motion Picture & Television Country House and Hospital in Woodland Hills, California.