Jack Flaherty competed at Cooperstown Dreams Park during Tournament 10 in 2006 and Tournament 11 in 2007, both times with the Sherman Oaks Riptide (CA). Over the course of both tournaments, his teams were 13-5 (6-3 in 2006, 7-2 in 2007).

Jack attended and graduated from Harvard-Westlake School (Studio City, CA). A four-year member of the varsity baseball team, he pitched and played short stop and third base. Jack recorded a 13-0 record from the mound during his junior year and went 10-0 his senior year. He completed the 2014 season receiving Gatorade Player of the Year for California.

Jack committed to play baseball at University of North Carolina (Chapel Hill, NC), however he was selected in the first round of the 2014 Major League Baseball Amateur draft by the St. Louis Cardinals. Jack made his major league debut pitching on September 1, 2014.

During the 2023 season, Jack was traded to the Baltimore Orioles. Prior to the 2024 season Jack signed with the Detroit Tigers before he was acquired by the Los Angeles Dodgers where he went on to help the team clinch the 2024 World Series title.