Timmerman was born in Cherokee, Iowa. He attended Washington High School in Cherokee, Iowa, and starred in football, basketball, and track. In football, he won All-Conference honors, and was an All-State Honorable Mention honoree. In track, he finished eighth in the state track meet on the 110 high hurdles as a senior. Adam Timmerman graduated from Washington High School in Cherokee, Iowa, in 1989.
After the 1998 season, Timmerman joined the Rams and won another Super Bowl ring in Super Bowl XXXIV. He also made it back to the Super Bowl with the Rams in Super Bowl XXXVI, losing to the New England Patriots. He became the first player to ever win and lose a Super Bowl with one team Green Bay Packers and win and lose a Super Bowl on another team St. Louis Rams. Timmerman was voted a Pro Bowl alternate four consecutive seasons (1999, 2000, 2001, and 2002) and twice (1999, 2001) he was called into duty to play in the Pro Bowl due to injuries to other NFC guards. The Rams released Timmerman on February 27, 2007, and he officially retired following the 2007 season.