Campbell was head coach of both the Atlanta Falcons (twice) and Philadelphia Eagles, as well as being defensive coordinator for both teams separate from his times as their head coach. He also served as defensive line coach for the Patriots (1962-1963), Vikings (1964-1965-1966), and Rams (1967-1968). He was an expert in the 3–4 defense; his Philadelphia Eagles defenses ranked first in the league in points allowed in 1980 and 1981, and second and first in yards allowed in those same years . Campbell has the third lowest winning percentage among head coaches who have coached more than three seasons in the NFL . The only coaches behind him are Bert Bell and David Shula.
Campbell spent two years in the United States Army between college and the NFL. He lives in St. Augustine, Fla., 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.