Originally a lawyer from New York City, Jennings Lang came to Hollywood in 1938 and set up an office as a talent agent. In 1940, he joined the Jaffe Agency and, within a few years, became the company's president and one of Hollywood's leading agents. He joined MCA in 1950 and, two years later, became vice president of MCA TV Ltd. In this capacity, he worked with Universal Studios and was involved in developing, creating and selling new series throughout the 1950s and 1960s, including Wagon Train (1957), The Bob Cummings Show (1955) and McHale's Navy (1962). Lang also played a key role in developing television movies as a staple of TV programming.

Lang produced and executive-produced theatrical films for Universal from 1969 to 1986, when his career was curtailed by a major stroke. Among them were Tell Them Willie Boy Is Here (1969), Play Misty for Me (1971), Charley Varrick (1973), Slaughterhouse-Five (1972), Airport 1975 (1974), Airport '77 (1977), Earthquake (1974), Rollercoaster (1977), Nunzio (1978), The Concorde... Airport '79 (1979) and The Sting II (1983). He is credited with helping launch the early careers of Clint Eastwood and Steven Spielberg and developing the technique of "Sensurround".