John Farrell's journey in professional baseball began when he was drafted by the Cleveland Indians in the second round of the 1984 MLB Draft. A right-handed pitcher, Farrell made his Major League debut with the Indians on August 18, 1987. Over the next few years, he established himself as a reliable starting pitcher. Farrell's tenure with the Indians lasted until 1990, during which he demonstrated his skills on the mound, despite battling injuries that occasionally sidelined him.

In 1991, Farrell was traded to the California Angels, where he continued to pitch in the Major Leagues. However, his time with the Angels was short-lived, as he was released by the team in 1992. Farrell's career faced a setback due to injuries, leading him to miss the entire 1992 and 1993 seasons. Despite these challenges, he made a comeback in 1993 with the Cleveland Indians, although his appearances were limited.

Farrell's playing career concluded with the Detroit Tigers in 1996. After retiring as a player, he transitioned into a coaching and executive role, which would define the next phase of his baseball career. Farrell joined the Cleveland Indians as a coach and later served as the team's Director of Player Development from 2001 to 2006. His work in this capacity was instrumental in shaping the future of the franchise, as he oversaw the development of young talent within the organization.

In 2007, Farrell took on the role of pitching coach for the Boston Red Sox. His expertise and leadership were integral to the team's success, culminating in a World Series championship in 2007. Farrell's ability to manage and develop pitchers was widely recognized, and he remained with the Red Sox until 2010.

The Toronto Blue Jays appointed Farrell as their manager in 2011. During his two-year tenure, he worked to improve the team's performance, although the Blue Jays did not reach the postseason under his leadership. In 2013, Farrell returned to the Boston Red Sox, this time as the team's manager. His return was marked by immediate success, as he led the Red Sox to a World Series title in his first year at the helm. This achievement underscored his ability to guide a team to victory on baseball's biggest stage.

Farrell managed the Red Sox until 2017, during which time he led the team to three American League East division titles. However, after the Red Sox were eliminated in the 2017 American League Division Series, Farrell was dismissed from his managerial position. His tenure with the Red Sox was characterized by both triumphs and challenges, reflecting the unpredictable nature of the sport.