In 1941, Boone joined the United States Navy and served on three ships in the Pacific during World War II, seeing combat as an aviation ordnanceman, aircrewman, and tail gunner on Grumman TBF Avenger torpedo bombers, and ended his service with the rank of petty officer first class.

[4] In his youth, Boone had attended the San Diego Army and Navy Academy in Carlsbad, California, where he was introduced to theatre under the tutelage of Virginia Atkinson.

"Serious" and "methodical", Boone debuted on the Broadway theatrical scene in 1947 with Medea, starring Judith Anderson and John Gielgud; it ran for 214 performances.

Elia Kazan used Boone to feed lines to an actress for a film screen-test done for director Lewis Milestone.

[citation needed] During the filming of Halls of Montezuma, he befriended Jack Webb, who was then producing and starring in Dragnet.

Boone's next television series, Have Gun – Will Travel, made him a national star because of his role as Paladin, the intelligent and sophisticated, but tough gun-for-hire in the late 19th-century American West.

The show had first been offered to actor Randolph Scott, who turned it down and gave the script to Boone while they were making Ten Wanted Men.

[9][10] He occasionally did other acting appearances such as episodes of Playhouse 90 and The United States Steel Hour and TV movie The Right Man (1960).

He had a cameo as Sam Houston in The Alamo (1960), a starring role in A Thunder of Drums (1961) and narrated a TV version of John Brown's Body.

[15] He returned to the mainland to appear in films such as Rio Conchos (1964), The War Lord (1965) with Charlton Heston, Hombre (1967) with Paul Newman, and an episode of Cimarron Strip.

Boone and others convinced Freeman that the islands could offer all necessary support for a major TV series and would provide an authenticity otherwise unobtainable.

Coincidentally, Lord had appeared alongside Boone in the first episode of Have Gun – Will Travel, titled "Three Bells to Perdido".

[24] In the early 1970s, Boone starred in the short-lived TV series Hec Ramsey, which Jack Webb produced for Mark VII Limited Productions, and which was about a turn-of-the-20th-century Western-style police detective who preferred to use his brain and criminal forensic skills instead of his gun.

Older now, he was the deputy chief of police of a small city in Oklahoma, still a skilled shooter, and carrying a short-barreled Colt Single Action Army revolver.

[2] In that year, he accepted an invitation from Israel's Commerce Ministry to provide the Israeli film industry with "Hollywood know-how".

He appeared in The Last Dinosaur (1977) and The Big Sleep (1978), and provided the character voice of the dragon Smaug in the 1977 animated film version of J. R. R. Tolkien's The Hobbit.

[31] Boone moved to St. Augustine, Florida, from Hawaii in 1970 and worked with the annual local production of Cross and Sword, when he was not acting on television or in movies, until shortly before his death in 1981.