Bourn was acquired from the D-backs in exchange for Minor League outfielder Jason Heinrich. The O's moved Joey Rickard to the 60-day disabled list to open a spot for Bourn on the 40-man roster.
Like Drew Stubbs, claimed off waivers from the Rangers on Wednesday, Bourn should give the Orioles some speed and defense. The duo will also provide insurance in the wake of center fielder Adam Jones' hamstring injury, which has kept him out of the lineup since Friday.
"Just all-around, can play all three positions. Left-handed, veteran guy who knows his way around," Showalter said of Bourn, who is batting .261/.307/.362 with 12 doubles, six triples, three homers and 13 stolen bases in 89 games.
"Got a great reputation as a teammate and professional and brings some things we are in need of and have been for a while with Adam [sidelined]. I am hoping [Jones] is ready to play Friday, but we've got to prepare for if he isn't. And Nolan [Reimold] has done a serviceable job for us [in center field], but it's a place we would like to be better at if possible. And he and Stubbs have a lot of experience there."
In an odd sequence of events earlier in the day, the Orioles added Stubbs and designated left-hander Kyle Lobstein, whom they acquired from the Pirates in exchange for lefty Zach Phillips just hours prior.
"We have a couple other discussions that we are working on and we will see if those come to fruition," Orioles executive vice president of baseball operations Dan Duquette said right before the Bourn news officially broke.
"We are happy to address our outfield defense with a defender who can help us in a number of positions, and also someone Buck can insert in a game and give us a good chance for a stolen base."
Duquette didn't offer a reason for adding Lobstein only to designate him shortly after. But if the lefty clears waivers, the O's could try to keep him in the organization.
Lefty Ashur Tolliver had been designated for assignment to make room for Lobstein on Baltimore's active roster.
"At this time of year, there's a lot of players moving around and deadlines," Duquette said. "You are trying to not only get your team ready, but get your roster ready in the event you advance to the playoffs. … That's what we are trying to accomplish there."
Stubbs, 31, has batted .259/.343/.414 (15-for-58) with three home runs, six RBIs and eight stolen bases over 39 games between the Rangers and Braves this season.
Lobstein, 27, was 2-0 with a 3.96 ERA in 14 games with the Pirates this season, holding left-handed hitters to a .083/.241/.083 slash line. He also posted a 4.11 ERA in 19 Triple-A appearances (six starts).
Tolliver, 28, was 1-0 with a 5.79 ERA in five games with the Orioles this season.