Byrnes grew up in Washington, D.C., where he attended and played second base for St. Albans School, breaking the single season hits record. He was recruited by Haverford College, where he was team captain and set records for home runs and RBI. He graduated in 1992 with a BA in English.
Cleveland Indians
Byrnes joined the Cleveland Indians in 1994 after a chance meeting at a Haverford College Alumni game with Ronald M. Shapiro, the father of Mark Shapiro, the team's general manager. He quickly worked his way up the organizational ladder, first as an intern, then as a video scout, and then to the position of Scouting Director in 1998. The Cleveland Indians won the American League Championship Series and advanced to the World Series in 1995 and 1997, as well as won Central Division titles in 1995, 1996, 1997, 1998 and 1999.
Colorado Rockies
In 1999, Byrnes was hired by colleague Dan O'Dowd to fill the assistant general manager position for the Colorado Rockies, where he was in charge of the farm and scouting departments.
Boston Red Sox
Byrnes joined the Boston Red Sox as assistant general manager in 2003 when he was recruited by the team's general manager, Theo Epstein. In his second season with the Boston Red Sox, the team won the 2004 World Series. It was the Red Sox' first World Series championship since 1918, ending what remains the third longest championship drought in the history of any Major League team, after the Chicago White Sox and the Chicago Cubs. In a 2005 interview with The Boston Globe, Epstein said of Byrnes, "He's a key voice in player personnel. He's got as much a feel for evaluating and statistical analysis as anyone in baseball.”
Arizona Diamondbacks
Byrnes joined the Arizona Diamondbacks as general manager in 2006, where he remained until July 1, 2010. He promoted A.J. Hinch to manager in 2009, a move considered unorthodox because of Hinch's prior position in player development. It was rumored that Byrnes was asked to resign when he was unwilling to fire Hinch. According to a 2016 story about Hinch by Ken Rosenthal of Fox Sports, Byrnes “actually was ahead of his time.” In the story, Rosenthal noted, “How did it work out for the industry, which reacted to the DBacks’ hiring of Hinch with almost universal disgust? I was one of many in the media who was critical of the move and Byrnes’ framing of it. But the rationales that made Hinch's hiring so controversial are now almost standard, barely drawing notice today.”
San Diego Padres
Byrnes joined the San Diego Padres as senior vice president of baseball operations in 2010. In 2011, he was promoted to general manager.
Los Angeles Dodgers
In 2014, the Los Angeles Dodgers announced Byrnes as the team's senior vice president of baseball operations. He was recruited by Andrew Friedman, the team’s new president of baseball operations. The new front office was “a force to be reckoned with” according to a story on Los Angeles’ ABC 7's website by Ramona Shelburne, who documented their meetings during the 2014 MLB Winter Meetings. The Dodgers won the National League pennant, advancing to the World Series, in 2017 and 2018. In 2017, the Dodgers finished the season with a major league best 104 victories.
