The 76ers drafted Jackson with the 4th overall pick in the NBA draft. He would play eight seasons (1964–1972) with the Philadelphia 76ers in the NBA. A 6-foot, 9-inch (2.06 m) power forward who played center occasionally, he was named to the NBA's 1964–65 All-Rookie Team after averaging 14.8 points and 12.9 rebounds per game. He played in the NBA All-Star Game the same season. A teammate of Wilt Chamberlain, Jackson was a starter on the 1966–67 Philadelphia championship team that scissored the Boston Celtics' string of eight straight NBA championships. After the 1968 season, Chamberlain was dealt to the Lakers, and Jackson (along with the acquired Darrell Inhoff obtained in the Wilt trade), were asked to fill the void. However, Jackson suffered a major injury in 1969 and was never the same player after that, missing a total of 66 games his last three years in the NBA.