Yovani Gallardo participant of 2017 Major League Baseball season
Seattle Mariners
On January 6, 2017, Gallardo was traded to the Seattle Mariners in exchange for Seth Smith. After struggling through the first half of the season for Seattle, Gallardo was moved to the bullpen on June 22. He was reinstated to the starting rotation in August due to his strong performance as a reliever and the many injuries that had been crippling the Mariners' starting pitching. However, due to several poor appearances and new pitching acquisitions, he was relegated to the bullpen once more. 
In 2017, he was 5–10, with a 5.72 ERA. He had his option declined on November 2, 2017, and became a free agent.