Seattle made the roster moves Thursday during an off day. Beimel had been with the Rangers during spring training but struggled, giving up 11 earned runs in three innings over four appearances. He was released by the Rangers on March 23.
Beimel was a standout last season in Seattle's bullpen. He was 3-1 with a 2.20 ERA in 56 appearances.
Montgomery was acquired in a trade with Tampa Bay earlier this week that sent right-handed starter Erasmo Ramirez to the Rays. Montgomery had one option remaining and will start the season in the minors, but could be an option as a starter or reliever down the road.