Born in June 1912 in Schenectady, New York, John McMullen Jr. was the son of Judge John McMullen and Leah McMullen, nee Campbell.
Initially, McMullen attended the University of Alabama, but he did not graduate. Instead, he ventured to New York City, where he pursued a career in acting, taking on character roles on and off Broadway.
McMullen was a respected figure in New York's theatre circles, serving as a teacher at the Fagan School of Theatre in Manhattan. He claimed to have taught notable students such as Mickey Rooney and Ann Miller. His theatre career, however, was interrupted by World War II, during which he was drafted and served as a combat engineer in the European theatre.
While in the Army, McMullen worked on a short film that would later change the course of his professional life. He became a scriptwriter, and one of his projects, "Toward Independence," a documentary about a one-legged Army Veteran, won the Academy Award for Best Short Subject Documentary in 1948. McMullen wrote the script and was the principal creative force behind the project, but he did not receive a co-directing credit and thus did not receive an Oscar statuette. He subsequently sued the Academy in 1949, seeking to be awarded a statuette, but lost the case.
McMullen continued to work as a scriptwriter, eventually landing a job with Granducci Scripts Inc. in Washington D.C. He wrote numerous film scripts for corporate clients on non-fiction subjects, staying with the company for 15 years before briefly becoming a freelance scriptwriter.
In 1968, McMullen was hired to head General Electric's film unit, relocating to his hometown of Schenectady. However, his tenure was short-lived, as he suffered a heart attack in 1968 and was forced to retire. McMullen passed away in January 1974 while undergoing heart surgery at Ellis Hospital. He was survived by his son, Douglas Jr., his wife Giovanna Belforti McMullen, and an older son from an earlier marriage, John.
