On February 8, 2008, Bédard was traded to the Seattle Mariners in a 5-for-1 deal sending outfielder Adam Jones and pitchers George Sherrill, Tony Butler, Chris Tillman and Kam Mickolio to the Orioles.
On February 13, Mariners manager John McLaren announced that he would be their Opening Day starter.
Bédard then signed a one-year, 7-million dollar deal with the Mariners on February 15, avoiding salary arbitration.
He was 6–4 with a 3.67 ERA in 15 starts for the Mariners in 2008 but on July 10, 2008, he was placed on the 15-day disabled list with stiffness in his left shoulder.
He missed the rest of the season and underwent arthroscopic surgery on the shoulder on September 26.

Bédard only played the first four months of the 2009 season before landing on the disabled list again due to a torn labrum in his pitching shoulder.
He finished with a 5–3 record and a 2.82 ERA.

On February 6, 2010, Bédard re-signed with the Mariners to a one-year contract with a mutual option for 2011.
At the start of the 2010 season, there was hope he would return to the majors as soon as May or June 2010.
Since then, he suffered multiple setbacks while rehabbing his shoulder and did not pitch in the majors in 2010, though he did appear in three minor league rehab games.

After the 2010 season, the Mariners declined their 2011 option on Bédard's contract and re-signed him to an incentive laden non-guaranteed contract.
He appeared in 16 games for the Mariners to start the 2011 season, with a 4–7 record and a 3.45 ERA.
On February 8, 2008, Bédard was traded to the Seattle Mariners in a 5-for-1 deal sending outfielder Adam Jones and pitchers George Sherrill, Tony Butler, Chris Tillman and Kam Mickolio to the Orioles. On February 13, Mariners manager John McLaren announced that he would be their Opening Day starter. Bédard then signed a one-year, 7-million dollar deal with the Mariners on February 15, avoiding salary arbitration. He was 6–4 with a 3.67 ERA in 15 starts for the Mariners in 2008 but on July 10, 2008, he was placed on the 15-day disabled list with stiffness in his left shoulder. He missed the rest of the season and underwent arthroscopic surgery on the shoulder on September 26.
Bédard only played the first four months of the 2009 season before landing on the disabled list again due to a torn labrum in his pitching shoulder. He finished with a 5–3 record and a 2.82 ERA.
On February 6, 2010, Bédard re-signed with the Mariners to a one-year contract with a mutual option for 2011. At the start of the 2010 season, there was hope he would return to the majors as soon as May or June 2010. Since then, he suffered multiple setbacks while rehabbing his shoulder and did not pitch in the majors in 2010, though he did appear in three minor league rehab games.
After the 2010 season, the Mariners declined their 2011 option on Bédard's contract and re-signed him to an incentive laden non-guaranteed contract. He appeared in 16 games for the Mariners to start the 2011 season, with a 4–7 record and a 3.45 ERA.
Érik Bédard