He worked for the Massachusetts Institute of Technology as director of its Center for Space Research; the National Aeronautics and Space Administration (NASA) as the director of its Lewis Research Center; the United States Air Force, where he served with the Strategic Air Command and as a member of the United States Air Force Scientific Advisory Board; North American Rockwell, where he oversaw the design and development of the Apollo command and service module that took the first men to the Moon, and the S-II of the Saturn V rocket.

[1] McCarthy worked as a project manager in the Aeroelastic and Structures Research Laboratory at MIT from 1951 to 1955, where he investigated the phenomenon of supersonic flutter, and developed the first tests for it.

[2] At North American he oversaw the design and testing of the Apollo command and service module that took the first men to the Moon, and the S-II of the Saturn V rocket that launched it.

He became the director of the National Aeronautics and Space Administration (NASA) Lewis Research Center in Cleveland, Ohio, in 1978.

[1] McCarthy returned to private industry in 1982 as the vice president and general manager of the Electro-Mechanical Division of Northrop Corporation in Anaheim, California.