A key member of the World Series winning Royals in 1985, Jackson made one of the most important starts in Royals history in the American League Championship Series. Trailing the Blue Jays three games to one and facing elimination, Jackson tossed a complete game shutout and kept the Royals alive. Two weeks later, in the '85 World Series, Jackson again took the ball with the Royals trailing three games to one in a Game Five, and again Jackson led the Royals to a crucial victory over the St. Louis Cardinals. Jackson's 1.04 post-season ERA with the Royals is the lowest in team history (min 10 IP). After disappointing seasons in 1986 and 1987, Jackson, along with Angel Salazar, was traded to Cincinnati for Kurt Stillwell and Ted Power.
He was elected to the National League All-Star team twice (1988 and 1994). He led the National League in wins in 1988 with 23 and, with 18-game winner Tom Browning, combined for the best pitching tandem in baseball that season. Jackson's great 1988 season went largely unnoticed because of the outstanding season turned in by the Dodgers' Orel Hershiser.
Jackson also played in three World Series for three teams: 1985 for the Kansas City Royals, 1990 for the Cincinnati Reds, and 1993 for the Philadelphia Phillies.