Gagné was originally drafted on June 2, 1994 by the Chicago White Sox, but did not sign and attended junior college instead. The following year he signed as an amateur free agent with the Los Angeles Dodgers on July 26, 1995.

After spending his first several seasons with the Dodgers' minor league affiliates, Gagné was called up to make his MLB debut on September 7, 1999. He played only five games with the Dodgers that season, pitching 30 innings and finishing with a 2.10 earned runs average.

Gagne continued to split his time between the Dodgers and the minors over the next two seasons, until earning a full roster spot in 2002. Gagné also earned his first of three MLB All-Star Game selections in 2002.

Gagné was recognized for his great play in 2003, winning the Rolaids Relief Man of the Year Award and Cy Young Award. In 2004, Gagné made his first post season appearance with the Dodgers, losing the National League Divisional Series to the St. Louis Cardinals.

Gagné missed considerable parts of the 2005 and 2006 after a back injury and Tommy John surgery to repair a sprained left elbow ligament. Following the 2006 season, Gagné signed as a free agent with the Texas Rangers on December 19, where he played for the first half of the 2007 season.

On July 31, 2007, Gagné was traded to the Boston Red Sox, where he completed the 2007 season and won the World Series with the Red Sox over the Colorado Rockies.

On December 9, 2007, Gagné signed with the Milwaukee Brewers. Just days later, on December 13, he was named in the Mitchell Report for his alleged steroid use.

1. Full name: Éric Serge Gagné
2. Born: January 7, 1976
3. Birthplace: Montreal, Quebec, Canada
4. 1995: Signed with Dodgers
5. 2003: Cy Young Award Winner
6. Named in 2007 Mitchell Report