A veteran of television and film westerns, he has portrayed two different participants in the legendary 1881 O.K. Corral gunfight between the Earps and the Clantons. In 1955, he played Ike Clanton in an episode of the television series "You Are There" (1953), and in 1957, he played Morgan Earp in the film Gunfight at the O.K. Corral (1957). On "Star Trek" (1966), the USS Enterprise away team beam onto a planet and he again finds himself at the O.K. Corral, playing Tom McLaury.
He plays a medic in The Man in the Gray Flannel Suit (1956). Foreshadowing things to come, his character says, "This man is dead, Captain".
Is one of only 32 actors or actresses to have starred in both the original "Star Trek" (1966) up to and including Star Trek VI: The Undiscovered Country (1991) and then in one of the spin-offs.
Of the four main "Star Trek" (1966) cast members (the others being William Shatner, Leonard Nimoy and James Doohan), he is the only one who never appeared in "The Man from U.N.C.L.E." (1964), "Twilight Zone" (1959) or "The Outer Limits" (1963).
Was the only original "Star Trek" (1966) series cast member never to write an autobiography.
His personal favorite episode of "Star Trek" (1966) was "The Empath".
Was the first primary cast member from "Star Trek" (1966) to pass away.
The tagline "I'm a doctor, not a..." has been quoted in almost every incarnation of "Star Trek" (1966) on film and television.
Reportedly disliked doing the animated "Star Trek" (1973) series because he was never recording his lines at the same time as William Shatner and Leonard Nimoy. Kelley did not like this because he never got to interact with them and develop any rapport, which made reading his lines all the more difficult.
Before landing the role of Dr. McCoy, he was offered the choice to play Mr. Spock. Years later, he played both for Star Trek III: The Search for Spock (1984).
Made both his first (Episode "The Corbomite Manoeuvre") and last (Star Trek VI: The Undiscovered Country (1991)) Star Trek appearances with Nichelle Nichols.
Shortly after Mr. Kelley's passing, "He's dead, Jim" was forever memorialized by being added in tribute to Dr. McCoy for two 1999 video games: StarCraft Expansion Set: Brood War (1998) (VG) and Shatner-oids, a spoof of the classic Atari game "Asteroids".
The "Enterprise" (2001) character, Admiral Maxwell Forrest played by Vaughn Armstrong, is named after him.