Pat made his debut in 1991 with the Toronto Blue Jays and played a large part in their World Series championships in 1992 and 1993. His best year, however, came in 1996 when he went 20-10 with a 3.22 ERA and 177 strikeouts to win the American League Cy Young Award, barely beating New York Yankees pitcher Andy Pettitte.
Since leaving Toronto in 1999, Pat has played for the St. Louis Cardinals and the Baltimore Orioles. In the off-season prior to the 2004 season, however, he resigned with the Toronto Blue Jays.