He hit a home run in his first major league at bat on September 2, 1997. Fullmer's best season came in 2000, while playing for the Toronto Blue Jays. In 133 games, he hit career bests in home runs (32), RBIs (104), and batting average (.295). Fullmer was a member of the World Series Champion Anaheim Angels in 2002.
Fullmer's final game at the major league level was during the 2004 season with the Texas Rangers. He spent nearly all of 2005 out of baseball healing from injuries, before joining the Charlotte Knights near season's end, though he never played for them and would eventually retire. He attended Montclair College Preparatory School where he played for Walter Steele. Fullmer went to high school with another future Major League player, Russ Ortiz, whom he played against in the 2002 World Series.