The club placed pitcher Joseph Ortiz on the 60-day disabled list, allowing it room to add Hanson to the roster.
The Rangers are hoping Hanson can put last season behind him and return to the form that made him one of the game's rising young pitchers just three years ago.
With Derek Holland's injury and absence, likely until midseason, the Rangers are searching for pitching depth and fifth-starter candidates. Hanson is now one of those as he heads to spring training. Rangers pitchers and catchers report Sunday.
Hanson is set to make $500,000 in base salary, which will increase to $2 million if he is on the Opening Day roster. He is on a split contract, making one salary in the big leagues and another in the minors.
Hanson, 27, was 4-3 with a 5.42 ERA in 73 innings last season, which included a stay on the bereavement list. Hanson told the Los Angeles Times he struggled while grieving for his stepbrother.
It wasn't long ago that Hanson was putting up consistent numbers. From 2009 to 2011, he had a 3.28 ERA in 77 starts (460 1/3 innings). He made 32 starts in 2010 and pitched 202 2/3 innings, but he's seen a drop in his fastball velocity since then, dipping under 90 mph.
Hanson has struggled the past two years, with a 4.76 ERA in 46 games (44 starts) with 217 strikeouts, 101 walks and a 1.482 WHIP.