A native of Lake Bluff, Illinois Rockwell studied at the Pasadena Playhouse, from which he obtained a master's degree. During World War II he enlisted in the US Navy for four years serving in Washington D.C. 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. He appeared in a 1959 Perry Mason episode “The case of the Deadly Toy” as love interest to the defendant Claire Allison as Dick Benedict. He also starred in the 1961 Perry Mason episode "The Case of the Misguided Missile" as an Air Force officer court-martialled on a murder charge. He later starred in the 1962 Perry Mason episode "The Case of the Lurid Letter" as Everett Rixby, a high school principal.
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.
Rockwell starred in his own ABC western-themed television series, The Man from Blackhawk in the 1959-1960 season. Rockwell was cast as the Blackhawk Insurance Company's key investigator, Sam Logan, who is assigned to weed out fraud in the payment of claims. He also played Sam Thompson in Thompson's Ghost, Tom Bennett in The Bill Cosby Show and Officer Russo in Adam-12.
In 1967 he played a littering tourist in the Lassie episode "Lassie's Litter Bit", an iconic episode which earned Lassie a trip to the White House to shake hands with then First Lady "Ladybird" Johnson who had used the famous collie in her Keep America Beautiful Campaign.
Later in his career, he appeared on episodes of Petticoat Junction (1970, episode: "Spare That Cottage", as Norbert Thompson), 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.
On January 25, 2003, Rockwell died of cancer at his home in Malibu at the age of 82. He was survived by his wife, Elizabeth (née Weiss), to whom he had been married since 1942, and the couple's five children.
