The 27-year-old Freeman was 2-0 with a 2.61 ERA in a career-high 44 relief appearances last season with the Cardinals. He pitched once against the Dodgers in the playoffs.
Rangers general manager Jon Daniels said he expects Freeman, who is out of minor league options, to make the opening day roster.
''He's got a good arm and the acquisition price was right,'' Daniels said. ''We'll bring him in here and give him an opportunity.''
The Texas pitching staff has been beset by health problems in spring training, including a season-ending injury to ace Yu Darvish.