Jonah James Bayliss (born August 13, 1980 in North Adams, Massachusetts) is a Major League Baseball relief pitcher in the Toronto Blue Jays organization. He is an alumnus of Trinity College in Hartford, Connecticut, and Lawrence Academy at Groton in Groton, Massachusetts.
Bayliss was originally a seventh-round draft pick of the Kansas City Royals in , and he made his major league debut with that team on June 21, . Bayliss pitched 11 2/3 innings in relief for the Royals that year, and then he and minor league reliever Chad Blackwell were traded to the Pittsburgh Pirates for starting pitcher Mark Redman on December 7.
On March 28, , the Pittsburgh Pirates designated Bayliss for assignment. According to Pirates manager Neal Huntington, "Bayliss is the type of player that teams should be looking for on the waiver wire. He has good stuff, but has struggled with control. If he can figure that out, he can be a very solid reliever."
On June 19, 2008, Bayliss was traded by the Pirates to the Toronto Blue Jays.