Robert Rockwell was a native of Chicago, Illinois. He studied at the Pasadena Playhouse, from which he obtained a master's degree. Dramatic roles often eluded him, however, after beginning his career as a contract player for Republic Studios he appeared, over his almost 50-year acting career, in more than 350 television episodes and, on stage, opposite José Ferrer in the 1946 Broadway production of Cyrano de Bergerac, and with Ginger Rogers during the 1960s in a San Diego production of Whitfield Cook's play A More Perfect Union.
Rockwell was a founding member of the California Artists Radio Theatre. He played standard leads in a couple of anti-Communist-era features, including Republic's The Red Menace (1949), in which he is cast as a returning veteran of World War II, who is duped by communists.
In the first episode of The Adventures of Superman, he played Superman's father Jor-El. In 1952, he was cast in the episode "The Porcelain Lion" of Kirby Grant's western aviation adventure series, Sky King. Rockwell appeared in several episodes of the NBC television anthology series The Loretta Young Show (1958), in which he played Loretta Young's husband. Rockwell made several guest appearances on Perry Mason during the run of the CBS series from 1957 to 1966.
Later in his career, he appeared on episodes of Growing Pains (1988–1990) and Beverly Hills, 90210 (1993). His appearances in commercials and voiceovers totaled more than 200, most notably as the armchair grandfather treating his grandson to a piece of candy in the 1995 version of the Werthers Original candy spot.
Robert Rockwell died in Malibu, California on January 25, 2003, aged 82 from cancer. He was survived by his wife, Elizabeth (née Weiss), to whom he had been married since September 26, 1942. The couple had five children: Susan, Alison, Robert Jr., Jeffrey, and Gregory. His granddaughter, Taylor Rockwell, the daughter of actress Alison Rockwell, is a visual effects coordinator.