Along with series creator Gene Roddenberry, Coon is given credit for the show's idealistic tone and for creating several key story and world-building elements that would become important parts of the ongoing franchise.

Thereafter, he remained in the Marines as a reservist while studying radio communications at Glendale Junior College, where he performed in a production of The Night of January 16th.

Following additional studies at the University of Iowa, he returned to active duty during the Korean War era in 1950, ultimately attaining the rank of sergeant.

Upon his demobilization in 1952, Coon found work first as a radio newscaster before turning to freelance writing under the mentorship of Los Angeles Times reporter Gene Sherman.

Beginning in 1956, Coon was primarily involved in scripting teleplays for popular Western and action television shows, including Dragnet (1951), Wagon Train (1957), Maverick (1957), and Bonanza (1959).

Together with the writer Les Colodny, Coon floated the idea for The Munsters (1964), as a satirical take on The Donna Reed Show (1958), to MCA chairman Lew Wasserman.

The result of this last, whose format was worked out by Allan Burns and Chris Hayward and whose characters and situations were developed by Norm Liebman and Ed Haas, was yet another hit show, under the creative auspices of Joe Connelly and Bob Mosher.

(The latter series, though it owed much to C. S. Forester's novels about Horatio Hornblower and Jonathan Swift's satire Gulliver's Travels, was sold to the NBC television network using the unofficial nickname of "Wagon Train to the stars".)

His credited creations for Star Trek include the Klingons and the Organian Peace Treaty (in "Errand of Mercy"), Khan Noonien Singh (in "Space Seed", where he adapted a Carey Wilber story), Zefram Cochrane (in "Metamorphosis"), the advancement and the definition of the Prime Directive in "The Return of the Archons" and "Bread and Circuses", respectively, the official naming of the United Federation of Planets itself in "Arena" (in which he inadvertently plagiarized a Fredric Brown story), and the official naming of Starfleet Command in "Court Martial".

Following arguments with Roddenberry over the tone of the installment "Bread and Circuses", partly a satire on the medium of television, Coon left the writing staff and designated John Meredyth Lucas as showrunner.

The movie was to serve as a pilot for a new series, but Roddenberry balked at a decision by NBC to eliminate the character of Jerry Robinson, Questor's human companion/mentor.

A chain smoker of cigarillos for most of his life, the man whom fellow writer/producer Glen A. Larson referred to as "the spirit and soul of Star Trek" died in July 1973 from complications of lung and throat cancer at the age of 49, just one week after being diagnosed.