[1] Before moving to Hollywood, he acted in Hamlet on stage in New York City, a last-minute substitute for the scheduled actor who failed to appear to portray Fortinbras.

[5] Hadley starred in two television series, Racket Squad (1950–1953) as Captain Braddock, and The Public Defender (1954–1955) as Bart Matthews, a fictional attorney for the indigent.

In 1959 he played Sheriff Ben Tildy in "The Texan" espisode "The Sheriff of Boot Hill", and was pitted against bad guys Denver Pyle cast as saloon keeper Joe Lufton and his gunslinging partner Charles Maxwell cast as Luke Stricker.

In 1958 he played the rapacious mining baron Mort Galvin in S1 E39 "The Sacramento Story" on Wagon Train.

Throughout his 35-year career in film, Hadley was cast as both a villain and a hero of the law, in such movies as The Baron of Arizona (1950), The Half-Breed (1952), Highway Dragnet (1954) and Big House, U.S.A. (1955), and narrated a number of documentaries.