Alderson is the son of Gwenny Parry Alderson and John Lester Alderson; the latter an Air Force pilot who flew missions during World War II, Korea and Vietnam, Alderson has two siblings, Kristy and Dave.
Alderson attended Dartmouth College on a NROTC scholarship and graduated in 1969. He attended Falls Church High School in Falls Church, Virginia. He then joined the United States Marine Corps and served a tour of duty in Vietnam. He received his Juris Doctor from Harvard Law School in 1976. After law school, he worked for Farella Braun & Martel in San Francisco, California.
Alderson is married to Linda Alderson, and has two children, Bryn and Cate, who both also went to Dartmouth, and 3 grandchildren. He also had a dog named Buddy who died in 2016.
Roy Eisenhardt, one of the firm's partners, left to become president of the Oakland Athletics when his father-in-law bought the team. In 1981, Alderson joined Eisenhardt to become the Athletics' general counsel and in 1983 was named the team's general manager, a position he held through 1997. Under Alderson, the Athletics' minor league system was rebuilt, which bore fruit later that decade as José Canseco (1986), Mark McGwire (1987), and Walt Weiss (1988) were chosen as American League Rookies of the Year. The Athletics won four division titles, three pennants and the 1989 World Series during Alderson's tenure.
In 1995, team owner Walter A. Haas, Jr. died and new owners Stephen Schott and Ken Hofmann ordered Alderson to slash payroll. As a result, Alderson began focusing on sabermetric principles toward obtaining relatively undervalued players. He was a mentor to his eventual successor as general manager, Billy Beane.
Alderson left the Athletics to work for Major League Baseball's commissioner’s office, where he was executive vice president for baseball operations between September 1998 and 2005.
Alderson served as CEO of the San Diego Padres from 2005 to 2009, with the team winning back to back division titles in 2005 and 2006. He lectured at the University of California, Berkeley Haas School of Business.
In 2010, Alderson had been working as commissioner Bud Selig’s point man to address the issues of the corruption of baseball in the Dominican Republic, the largest supplier of Major League Baseball talent outside the United States.
Alderson was hired by the New York Mets after the 2010 baseball season to replace Omar Minaya as general manager. He was officially introduced as the general manager of the team on October 29, 2010, signing a four-year deal with a club option for 2015. Mets owner Fred Wilpon, was dealing with his involvement in the Madoff investment scandal, and Alderson worked with a limited budget. As Alderson was Billy Beane's predecessor and mentor with the Oakland A's, and as the Mets also hired Beane's former associates Paul DePodesta and J.P. Ricciardi to the front office, the team was jokingly referred to as the "Moneyball Mets".
The first big money signing that Alderson did with the Mets was a 7-year contract extension for David Wright in December 2012 which was worth $138 million (7 years for $122 million plus a club option for $16 million that the club picked up for the 2013 season). Wright's deal was contrary to the Mets budget-conscious policy of not giving huge contracts to players in their 30s; nonetheless Alderson made an exception as he viewed Wright as a leader and role model, on and off the field. Although it had been six years since the Mets' last playoff appearance and four years since their last winning season, Alderson managed to persuade Wright to stay as the Mets' farm system had young talented pitchers.
From 2012 to 2014, Alderson reduced the Mets payroll to under $100 million, and exchanged veterans to acquire young talent such as Zack Wheeler, Noah Syndergaard and Travis d'Arnaud. Alderson also developed players drafted by Minaya such as Matt Harvey, Jacob deGrom and Steven Matz.
The Mets won the National League pennant in 2015, making their first World Series appearance since 2000.