Hernandez opted out of his minor-league contract with the Mariners on Thursday, Jon Heyman of the New York Post reports.
Hernandez signed a minor-league contract with the Mariners on Friday, Daniel Alvarez-Montes of ElExtraBase.com reports.
Hernandez was released by the Tigers on Tuesday.
The Tigers reassigned Hernandez to minor-league camp Monday.
Hernandez has looked good this spring and could earn an Opening Day bench role with the Tigers, Jason Beck of MLB.com reports.
Hernandez agreed Wednesday with the Tigers on a minor-league contract that includes an invitation to MLB spring training, Jon Heyman of the New York Post reports.
Hernandez went 1-for-4 with a stolen base in the first game of Tuesday's doubleheader against the Mets.
Hernandez will start in left field and bat sixth in Monday's game against the Mets.
Hernandez is not in the lineup for Tuesday's game against the Orioles.