Robles signed a major-league contract with the Mariners on Tuesday and was added to the team's active roster.
Robles and Seattle came to terms on a deal just days after the veteran outfielder was waived by Washington. He slashed .120/.281/.120 in 33 plate appearances with the Nationals and figures to serve as the primary backup to Julio Rodriguez in center field while mixing in at the other outfield positions against RHP.