He played in three regular season games in his NFL career: one with the Steelers in 2004, one with the Arizona Cardinals in 2009, and one with the Carolina Panthers in 2010, the latter being his only start.

After his playing career, he became the head coach of his alma mater St. John's Preparatory School in Danvers, Massachusetts.

[1] Due to an injury to Hasselbeck, St. Pierre was the starting quarterback in BC's 2000 season opener against Notre Dame.

St. Pierre spent the remainder of the season as a backup, however coach Tom O'Brien used him for at least one possession of every game.

St. Pierre went 25-of-35 for 342 yards, three touchdowns and no interceptions in the final game of his collegiate career, a 51–26 win over Toledo in the 2002 Motor City Bowl.

He came in and ran for a key first-down conversion late in the fourth quarter on a two-yard naked bootleg in the season finale against the Buffalo Bills.

[6] St. Pierre was allegedly one of the Pittsburgh players impersonated by a con man, Brian Jackson in 2005, along with Jerame Tuman and Ben Roethlisberger.

[12] On March 27, 2008, St. Pierre signed a one-year contract with the Arizona Cardinals, where he played for former Steelers and Los Angeles Chargers offensive coordinator Ken Whisenhunt.

He was the Cardinals third quarterback for all 16 regular season games and all four postseason contests, including Super Bowl XLIII.

This was in light of rookie quarterback Jimmy Clausen being diagnosed with a concussion after a loss to the Tampa Bay Buccaneers the previous Sunday.

In 2014, St. Pierre became head football coach at his alma mater, St. John's Preparatory School in Danvers, Massachusetts.