Guilmet takes the bullpen spot of T.J. McFarland, who was optioned to Norfolk after throwing three innings on Sunday. The Orioles also considered Josh Stinson, who's on 40-man roster, and Steve Johnson, who threw 89 pitches for Norfolk on Thursday.
Guilmet came up through the Indians' organization and reached the majors for the first time last season, appearing in four games for Cleveland and posting a lofty 10.13 ERA.
In 12 appearances for the Tides this season, Guilmet was 2-1 with a 5.65 ERA and 17 strikeouts.
Baltimore manager Buck Showalter said the biggest factor in Guilmet's promotion was that he was ''rested and pitching well'' and could give the team at least two innings on Monday.