He earned a degree from the University of Southern California after serving as an intelligence officer in the Army Air Force during World War II.

His character, Dr. Carrington, the unofficial leader of an Arctic polar expedition, observes the nearby crash of an unidentified flying object, and urges his military counterparts to communicate with the creature inside, even at the cost of their own lives.

Similarly, Cornthwaite appeared as Dr. Carrington opposite Ken Tobey (again as Hendry) in a spoof titled Attack of the B Movie Monster, shot in 1984.

Balancing his theater work with "bill-paying" jobs, he appeared frequently on television, including a role as naturalist John James Audubon in three episodes of the Desilu Studios Production, The Adventures of Jim Bowie, starring Scott Forbes.

He also made appearances during the 1950s, 1960s and 1970s in such series as Perry Mason, The Andy Griffith Show, The Untouchables, Crossroads, The Californians, Rescue 8, The Twilight Zone, The Roaring 20s, The Rifleman, Death Valley Days, Gunsmoke, Voyage to the Bottom of the Sea, Batman (episodes 35 and 36), The Monkees, Gidget, Laverne & Shirley, Dragnet, Combat!, The Munsters, Laredo, Kate and Allie, and Get Smart, in which he had a semi-recurring role as CONTROL's lab scientist, Professor Windish.

[4] Cornthwaite died at the Motion Picture and Television Country House and Hospital in Woodland Hills, Los Angeles, California, aged 89, on July 20, 2006.