On June 1, 2010, American baseball first baseman, Mark McGwire and Stephanie McGwire had three daughters by Cesarean section, and named them Monet Rose, Marlo Rose and Monroe Rose.

McGwire married Stephanie Slemer—a former pharmaceutical sales representative from the St. Louis area—in Las Vegas on April 20, 2002.

They reside in a gated community in Shady Canyon, Irvine, California. Together they created the Mark McGwire Foundation for Children to support agencies that help children who have been sexually and physically abused come to terms with a difficult childhood.

Mark has a son, Matthew (borb in 1987), from a previous marriage (1984–1990, divorced) to Kathleen Hughes.

His Major League Baseball (MLB) playing career spanned from 1986 to 2001 while playing for the Oakland Athletics and the St. Louis Cardinals, winning one World Series championship each, with Oakland as a player in 1989 and with St. Louis as a coach in 2011.

One of the most prolific home-run hitters in baseball history, McGwire holds the major-league career record for at-bats per home run ratio (10.6), and is the former record holder for both home runs in a single season (70 in 1998) and home runs hit by a rookie (49 in 1987).