Growing up, Keri was an avid fan of the Montreal Expos, something he attributes to his grandfathers' love of baseball. He remains one today despite the team's 2005 relocation to Washington to become the Washington Nationals.
Keri co-wrote and edited the book Baseball Between the Numbers: Why Everything You Know About the Game Is Wrong. He also wrote the New York Times BestsellerThe Extra 2%: How Wall Street Strategies Took a Major League Baseball Team from Worst to First, about the Tampa Bay Rays.
In March 2014, he published Up, Up, and Away: The Kid, the Hawk, Rock, Vladi, Pedro, le Grand Orange, Youppi!, the Crazy Business of Baseball, and the Ill-fated but Unforgettable Montreal Expos, which details the franchise history of the Expos. The book was a No. 1 Canadian bestseller.
Keri also appeared as himself during the first season of the IFC series Brockmire in the episode titled "Old Timers Day."
Arrest and criminal charges
Keri was arrested for allegedly assaulting his wife on July 18, 2019. 
He was granted bail the next day after being charged with three counts of assault causing bodily harm and uttering death threats. Court documents said the alleged attacks took place in July 2018, May 2019, and July 2019. The couple married in July 2018. Hours after his court appearance, The Athletic announced Keri was suspended "pending further information." 
^Jonah Keri, Up, Up, and Away: The Kid, the Hawk, Rock, Vladi, Pedro, le Grand Orange, Youppi!, the Crazy Business of Baseball, and the Ill-fated but Unforgettable Montreal Expos, Random House Canada, 2014, ISBN978-0307361356.