During his rookie season he helped the Cardinals win the 1987 NL Pennant. He also led the National League in Hit Batsmen (10).
He led the National League in ERA (2.18) in 1988, despite winning only five games (losing nine). He finished 4th in voting for the 1989 NL Cy Young with an 18-9 win-loss record, a 2.91 ERA and only 5 home runs surrendered in 2342⁄3 innings.
An injured elbow in 1990 cost him almost all of the next two seasons and most of his effectiveness, and Magrane never really regained his early form. He did win 11 games between the St. Louis and California ballclubs in 1993, but could not muster more than 2 wins or 74 innings pitched in any other season until his retirement in 1996 at the relatively early age of 32.