Born in Salt Lake City, Utah, Kearns moved with his family to California when he was very young. His mother was Cordelia M. Kearns (née Peterson; 1877–1962), a concert Pianist, from whom Kearns derived his love of music. He and his family were strict Mormons, whose ancestors were Mormon pioneers. His acting career began in 1916 when he joined 'The Rising Generation", a vaudeville troupe of eleven children that toured for 14 months. He briefly tried his hand at wool buying and worked for his father for a year. Kearns traveled the West as a representative of Howell, Jones and Donnell of Boston. His wool-buying career came to an abrupt end when Kearns purchased five boxcars full of black wool from a breed called Karakul for $8,000. The Problem was that black wool could not be dyed and no one knew how to use it in those days. After this fiasco, Kearns gladly gave up the wool Business and pursued a show Business career.

Kearns never married nor had any children. Describing himself as a night owl who hated to get up early in the morning, Kearns enjoyed cooking, reading novels, writing, traveling, going to the movies, and playing cards in his spare time. He was a member of the exclusive Societe des Gentilhommes Chefs de Cuisine, a club for the gentlemen chefs. The members traded original recipes with other club members. Kearns also wrote plays and scripts for his various radio shows. His favorite hobby was playing the organ. Kearns, who was musically trained by his mother, had played the pipe organ for a Los Angeles theatre in the 1930s. Kearns purchased a Hammond organ and installed it in a studio apartment he designed and built in the 1940s. He later purchased a larger 26 rank Wurlizter organ that had been designed for Warner Brothers in 1929. He then designed and built a soundproof 2-1/2 story home around the organ. Kearns delighted in playing the organ for his guests.

Kearns made his film debut in Hard, Fast and Beautiful (1951). He was the voice of the Doorknob in Disney's animated film, Alice in Wonderland (1951). Kearns appeared in other movies, making his final film appearance as the crime Photographer in Anatomy of a Murder (1959).

On television, Kearns reprised his radio roles on The Jack Benny Program and also appeared with Eve Arden and Richard Crenna in Our Miss Brooks (1953–55), first as Assistant Superintendent Michaels and later (in eight episodes) as Superintendent Stone, a role that he had played on radio.

He appeared on The George Burns and Gracie Allen Show a total of 11 times, Adventures of Ozzie and Harriet a total of 16 times, I Love Lucy, My Little Margie, Perry Mason, I Married Joan, December Bride, It's a Great Life, Angel, Gunsmoke, and General Electric Theater. Kearns played Fred on Professional Father. In 1959 Kearns appeared as criminologist Edward Langley in the Perry Mason episode, "The Case of the Perjured Parrot".

Kearns suffered a cerebral hemorrhage on February 11, 1962, during the third season of Dennis the Menace. He was hospitalized but never regained consciousness and died on February 17, 1962, five days after he had turned 55. He was buried at the Forest Lawn, Hollywood Hills Cemetery in Los Angeles.