The left-handed-hitting backstop was claimed off waivers by the Mariners in mid-March after the White Sox optioned him. He impressed the Mariners by hitting .375 with one home run and two RBIs in 16 Cactus League at-bats this spring, but the club chose to go with fellow left-handed hitter Steve Clevenger as the backup to Chris Iannetta on the final 25-man roster.
Brantly has played 112 games in the Majors for the Marlins and White Sox from 2012-15, posting a .225/.286/.317 line with five homers and 32 RBIs in 356 at-bats.
He'll join Mike Zunino as the Mariners catchers in Tacoma.
• Left fielder Norichika Aoki didn't start Wednesday's game vs. the Rangers after fouling a ball off his shin in Tuesday's 10-2 win over Texas, but is expected to return to the lineup for Friday's home opener. Luis Sardinas made his first career start in left field in Aoki's place.
• Kyle Seager slotted into the No. 2 spot in the lineup on Wednesday as the Mariners faced a right-handed starter for the first time. Switch-hitting shortstop Ketel Marte hit second behind Aoki in the first two games against lefty starters.
"It's probably going to be that way for a while," manager Scott Servais said of hitting Seager second against right-handers. "It's not a normal lineup with Aoki out, but I like him in the two-hole, and I've said all along, I don't think Kyle cares where he hits. He's going to give you a good at-bat."
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.