Detwiler, who was acquired from the Washington Nationals for two minor-leaguers on Dec. 12, made $3 million last season.
Detwiler pitched out of the bullpen in 2014 and finished 2-3 with a 4.00 ERA over 47 appearances. One of the main reasons the Nationals made the trade was because of their surplus of starters in their rotation and Detwiler's desire to leave the bullpen.
The Rangers will give Detwiler an opportunity to become the No. 3 or No. 4 starter in 2015. Detwiler made 13 starts in 2013 and pitched into the seventh inning three times, going 2-0 with one no-decision. Overall, he went 2-7 with a 4.04 ERA, but he missed nearly two months of the 2013 season with a strained oblique and a pinched nerve.