Nady passed his physical and finalized the deal with Seattle on Wednesday. He'll report to extended spring training at the Mariners complex in Peoria, Arizona.
Nady played in 22 games for the Padres, but hit just .135 with three homers and four RBIs. He had only five hits total in 50 at-bats with the Padres before being designated for assignment on May 5. He became a free agent on May 11.
Nady is a career .268 hitter, but has not played more than 100 games in a season since 2010 with the Chicago Cubs.