The Rangers signed Pena, 36, to a minor-league deal on Tuesday, and he will be active at Triple-A Round Rock either Tuesday or Wednesday.
Injuries to Prince Fielder and Mitch Moreland have forced the club to look at creative ways of filling the first-base position. There now are Brad Snyder, who has played most of his career in the minors, and Donnie Murphy, who never had played the position before and had to borrow a first-base glove from a teammate just a few weeks ago.
Pena must prove himself at Triple-A before the club considers promoting him. He last hit .209 for the Houston Astros and Kansas City Royals (just three plate appearances there) in 2013 with eight homers and 25 RBIs. He was an All-Star in 2009 with the Tampa Bay Rays, batting just .227, but mashing 39 homers and driving in 100 runs.
Pena, who was ninth in MVP voting in 2007 and '08, made his big league debut with the Rangers in 2001 after the club drafted him 10th overall in 1998. He has a career .233 average with 285 home runs with eight different teams.
Pena was in spring training with the Los Angeles Angels, going 5 for 26 with no homers and two RBIs before getting released March 23.