Schwarz's background in mathematics is considered unique among sports journalists, and this training has been deemed vital to his reporting of football brain issues. Schwarz's father taught him how to compute square roots when he was 4 years old. He became interested in baseball at age 11, in August 1979, when he purchased his first pack of baseball cards. Although Schwarz has described himself as "terrible" at baseball, he wanted to participate in the sport off the field and wound up as the statistician for his Scarsdale High School baseball team.

A 1986 graduate of Scarsdale High School, Schwarz graduated cum laude from the University of Pennsylvania in 1990 with a B.A. in mathematics. Schwarz also wrote for the sports section of the school newspaper, The Daily Pennsylvanian. He decided to pursue a career in journalism rather than to follow his original plan of becoming a high school or college math teacher.

Schwarz spent five months at The National Sports Daily before being hired by Baseball America in 1991, where he served as the senior writer until he joined the Times in March 2007.

He covered baseball exclusively from 1991 through 2006, writing not only for Baseball America but ESPN The Magazine, Newsweek and many other national publications. As a contributing freelancer to the Times, he helped begin the Sunday biweekly column "Keeping Score" — along with current Times business columnist David Leonhardt — where they applied statistical analysis to ongoing sports news. He also was the very popular host of ESPN's Baseball Today, the No. 1 rated individual-sport podcast on iTunes in 2006.

In 2004, Schwarz published his first book, The Numbers Game: Baseball's Lifelong Fascination with Statistics. The book covers the history of statistical analysis in baseball, including the stories of Henry Chadwick and Bill James, and the development of The Baseball Encyclopedia in the 1960s. Drawing widespread acclaim, the book was named by ESPN the "baseball book of the year" in 2004. His second book, Once Upon a Game: Baseball's Greatest Memories, was published in April 2007.

Schwarz's series on football concussions began in January 2007 with the discovery of trauma-induced damage in the brain of former Philadelphia Eagle Andre Waters, who recently had committed suicide at the age of 44. The series evolved to examine not just the NFL but the dangers of concussions in high school and other youth sports, including girls' soccer and basketball.

Subsequently, the U.S. House Judiciary Committee devoted three hearings to the issue of sport-related brain injuries, repeatedly citing Schwarz's work during them. In November and December of 2009, the NFL revamped its rules regarding concussion management, suspended its study of retired players' cognitive decline which Schwarz had exposed as improperly designed, and accepted the resignations of the two co-chairmen of a league committee that had conducted questionable research. The N.F.L. also began running the first public service announcement warning young athletes about the dangers of concussions. Following this, state legislatures all over the nation began the process of enacting statutes to require education and stronger rules to keep young athletes safer.

Schwarz lives with his wife Laura and son Teddy in New York City.

Alan Schwarz, The Numbers Game : Baseball's Lifelong Fascination with Statistics. New York: St. Martin's, 2004 & 2005. ISBN 0312322232.

Alan Schwarz, Once Upon a Game: Baseball's Greatest Memories. Boston, MA: Houghton Mifflin, 2007. ISBN 978-0618731275.