On November 22, 2003, Garciaparra married Olympian and World Cup Champion soccer star Mia Hamm. The couple has twin girls, Grace Isabella and Ava Caroline, who were born on March 27, 2007, in Los Angeles. The couple also welcomed their first son named Garrett Anthony born in January 2012.
On October 7, 2005, Garciaparra and his uncle Victor Garciaparra were alerted to the screams of two women who had fallen into Boston Harbor outside his condominium. One of the women sustained injuries to her head after hitting the pier on her way in. Garciaparra quickly jumped into the harbor and saved both women, who were later taken to the hospital.