The Mariners selected Garver's contract from Triple-A Tacoma on Wednesday.
Garver re-signed with Seattle as a non-roster invitee after camp opened and beat out Jhonny Pereda and Andrew Knizner for the backup catcher job. The 35-year-old will see some starts at catcher on days Cal Raleigh serves as the designated hitter, but Garver's playing time should be fairly limited.