Jackson was the Rams' 12th-round pick in 1968. He rarely played (2 games) in his rookie season.
In July 1969 he was traded to the Eagles for disgruntled running back Izzy Lang. Jackson immediately assumed a starting spot in the Eagles' lineup, and caught 65 passes while leading the NFL with 1116 receiving yards in 1969.
Harold played every game in his 4 seasons with the team, starting all but 2 games. He made the Pro Bowl as an Eagle in '69 and '72.
In 1972 he led the NFL in both catches (61) and receiving yards (1048).
Jackson returned to the Rams in June 1973 as part of the Roman Gabriel trade. He made 3 more Pro Bowls in his 5-year 2nd stint with LA. He later played for the Patriots, Vikings, and Seahawks,
(Jackson was replaced in the Eagles' lineup by Harold Carmichael, who then led the NFL in catches and yards in his first season as a starter.)