Jonathan Papelbon was a fourth round selection in the 2004 amateur draft. He spent three years in NCAA baseball pitching out of the bullpen for Mississippi State. He tallied a 2.90 ERA and 13 saves in his college years, being drafted after both his sophomore and junior seasons before finally signing joining the Red Sox organization. Papelbon brought them an explosive mid-90s fastball that would single-handedly carry him through most of his minor league career.

Jonathan Papelbon began his professional career in 2003 as a member of the Lowell Spinners, a single-A minor league team in the Red Sox system. He struggled at first, posting a 6.34 ERA, but he finished with 36 strikeouts in 32.2 innings. The Red Sox decided to use Papelbon as a starting pitcher for his early minor league career and he made six starts in 2003.

Papelbon's first full season in the minors took place in 2004 with the Sarasota Red Sox of the advanced A-ball Florida State League. He took nicely to his newfound role as a starter, striking out 153 batters in 129.2 innings with a 2.64 ERA in 24 starts. He would remain in a starting role for only one more season as his rapid development had him zipping through the Red Sox minor league system.

Perhaps the most important part of Papelbon's development came from the time he spent learning from then Red Sox ace Curt Schilling. Along with a new appreciation for how to attack hitters, Schilling helped Papelbon develop a splitter which almost immediately became a wipeout pitch. In 2005, Papelbon began the season in AA with a very talented Portland Sea Dogs team that along with Papelbon included the likes of Dustin Pedroia, Jon Lester, and Hanley Ramirez. Papelbon threw 87 excellent innings with a 2.48 ERA before his first promotion of the season.

Shortly after his promotion to AAA Pawtucket, Papelbon was called upon to make a spot start for the Boston Red Sox. Making his Major League debut on July 31, 2005, Papelbon held the Minnesota Twins to two earned runs in 5.1 innings while striking out seven and making a positive impression. Papelbon rejoined the Red Sox in August, making two more starts before moving back into the relief role that he played in college. He finished with a 2.65 ERA and 34 strikeouts in 34 innings with the Red Sox, adding four scoreless innings in the playoffs.

Earning a permanent spot in the majors, Jonathan Papelbon became Boston's fulltime closer in the 2006 season. On April 29, 2006, he set a major league record with his 10th save, against the Tampa Bay Devil Rays. No rookie in major league baseball history had recorded that many saves in the month of April. The 25-year-old closer finished 2006 with one of the most dominant seasons ever for a rookie reliever. Papelbon saved 35 games, struck out 75 batters in 68 innings, and held opposing batters to a .167 batting average. He put up brilliant numbers including a 0.92 ERA and .167 opponents' batting average in 68.1 innings. He finished second in the Rookie of the Year voting and made his first All-Star game.

Papelbon made each of the next three AL All-Star teams, giving him a total of four All-Star appearances in his four full seasons. His shining moment came in 2007. Following his dominant rookie year, Papelbon was great again with 37 saves and 84 strikeouts in 58.1 innings. In the playoffs, he shut down all of the competition, throwing 10.2 shutout innings and recording the final out of the 2007 World Series to become a champion just three years removed from A-ball.

In 2008, Papelbon agreed to terms with the Red Sox for $775,000. Papelbon's deal set the record for the largest contract for a closer not eligible for salary arbitration, topping Mariano Rivera's previous record by $25,000. Boston was under no obligation to pay Papelbon more than the league minimum of $390,000. Papelbon recorded his 100th career save on July 13, 2008. Among pitchers who have thrown at least 200 innings, Jonathan Papelbon's 0.930 WHIP through 2008 is the lowest in major league history.

In 2009, Papelbon agreed to a one-year $6.25 million contract with the Red Sox, avoiding arbitration. This is the largest contract for a closer in his first year of arbitration eligibility. In 2009, Papelbon passed Bob Stanley to become Boston's all-time leader in saves. In 2010, he blew eight saves, leaving the possibility of him being traded elsewhere. The Red Sox ended up keeping Papelbon as their closer, and his productivity improved over the 2011 season.

On June 7, 2011, Papelbon recorded his 200th career save against the New York Yankees, and achieved the mark in the fewest number of appearances (359), beating Mariano Rivera's mark in 382 appearances. For the 2011 season, Papelbon recorded 31 saves in 34 opportunities. He blew just 3 saves all season long, but 2 occurred during the final month of the season, including the final game of the 2011 regular season. Following the 2011 World Series, Papelbon became a free agent and signed with the Philadelphia Phillies.