Campbell was head coach of the Atlanta Falcons (twice) and Philadelphia Eagles as well as the defensive coordinator for each team separate from his times as head coach. He also served as defensive line coach for the Boston Patriots (1962–1963), Minnesota Vikings (1964–1966), and the Los Angeles Rams (1967–1968). He was an expert in the 3–4 defense; his Eagles defenses ranked first in the league in points allowed in 1980 and 1981, and second and first in yards allowed. At 46 games under .500, Campbell's 34–80–1 head coaching record is the fifth lowest winning percentage among head coaches who have coached five seasons in the NFL. The only coaches with worse winning percentages are Phil Handler, Bert Bell, Carl Storck, and David Shula.
Campbell spent two years in the United States Army between college and the NFL. He lived in St. Augustine, Florida with his wife, the former June Roberts. The Campbells have two children: a daughter, Alicia Johnson, and a son, Scott. In 2013, Campbell fell and broke multiple vertebrae in his neck. He died on July 13, 2016.