His brother, Francis Joseph McCarty, developed an early radiotelephone system,[2] before dying in a 1906 accident.

John P. McCarthy continued promotion, but was unsuccessful in marketing this invention,[3][4] and entered the film industry in 1914.

[6] McCarthy moved behind the camera in 1920, writing, producing and directing Out of the Dust, starring Russell Simpson.

[13] His most prolific year was 1931, when he directed eight films, two of which he also wrote: Cavalier of the West and God's Country and the Man.

[15] In 1946 McCarthy wrote the story for the Western, Under Arizona Skies, directed by Lambert Hillyer, which was his final film credit.