Smith spent nine seasons in the NFL as a defensive end. He was the first overall selection in the 1967 NFL draft, chosen by the Baltimore Colts. The Colts won Super Bowl V at the end of the 1970 season, earning Smith his only Super Bowl ring. He was traded to the Oakland Raiders before the 1972 season, and finished his career with the Houston Oilers. He was selected All-Pro one year, All-Conference two years, and went to two Pro Bowls.