John David Baker
- Bats Left, Throws Right
- Height 6' 1", Weight 210 lb.
- School University of California
- High School De La Salle High School (Concord)
- Debut July 9, 2008
- Final Game September 28, 2014
- Born January 20, 1981 in Alameda, CA, USA
John made his major league debut with the Florida Marlins in 2008 after a trade for minor leaguer Jason Stokes at the end of spring training 2007. He hit .299 in 61 games in his first season in the majors, then became the Marlins' regular catcher in 2009, when he played 112 games and hit .271 with 25 doubles, 9 homers and 50 RBI. He only saw limited playing time in 2010 and 2011, and hit only .154 the latter year. Following that season, he was traded to the San Diego Padres for pitcher Wade LeBlanc. He was San Diego's main backup catcher in 2012, hitting .238 in 63 games, but fell to .150 in 16 games in 2013 and lost his job, then was claimed off waivers by the Los Angeles Dodgers on June 15, ending the season in the minors.
Playing for the Chicago Cubs on July 29, 2014, he was the winning pitcher in the longest game in team history, a 16-inning, 4-3 win over the Colorado Rockies that took 6 hours, 27 minutes to complete. Pressed into mound duty in the top of the 16th, he retired Charlie Culberson on a pop-up, then walked Drew Stubbs but got Cristhian Adames, who was playing his first big league game, to hit into an inning-ending double play. He led off the bottom of the inning with a walk against Tyler Matzek and advanced to second on a sacrifice bunt by Emilio Bonifacio; Arismendy Alcantara was hit by a pitch and Anthony Rizzo singled to load the bases before Starlin Castro ended the marathon with a sacrifice fly to right. Baker had never pitched as a professional, but Cubs starter Edwin Jackson had lasted only 4 innings, and the team had already used 7 relievers and most of its bench, including starting pitchers Travis Wood and Jake Arrieta, who both pinch-hit. John retired after playing 17 games for the Tacoma Rainiers, in the Seattle Mariners organization, in 2015. In December, he was hired by the Cubs to work as a baseball operations assistant. He remained with them through 2020, when he was a mental skills coach.
In November 2020, the Pirates hired him to run their minor league system, replacing Larry Broadway.