Martinez, a 12th-round pick by the San Diego Padres in the 2007 First-Year Player Draft, joins Matt Wieters, Taylor Teagarden and Luis Exposito on the Orioles' 40-man roster.
Martinez, 27, is a career .272/.362/.364 hitter in six minor league seasons in the Padres (2007-11) and Rangers (2012) systems. In 2012, he batted .270/.350/.386 in 65 games with Triple-A Round Rock and also appeared in 10 games for the Rangers, going 2-for-18.
Martinez, a native of Miami, Fla., went 12-for-59 with a double, triple, home run and 10 RBIs in 22 games with the Padres in 2011.
"He's been a pretty good hitter in the minors," said Orioles executive vice president Dan Duquette. "He's got a good arm. He's a good defensive catcher. And he gets on base. He gives us a little more of a presence at the catching position. He's handled pitchers well over the course of his career."
The Orioles will temporarily lose catchers Allan De San Miguel (Australia) and Chris Robinson (Canada) to the World Baseball Classic during spring training. They could decide later to add Caleb Joseph and Brian Ward as non-roster invites.
The Orioles' 40-man roster is now full.