The Rangers optioned reliever Anthony Ranaudo to Triple-A to make room for Martinez on the 25-man roster.
Martinez (5-5, 3.43 ERA) made 16 starts for the Rangers before being sent to Round Rock on July 2. Martinez has tossed at least six innings in seven of his last eight starts for Texas. He pitched a combined six innings in two starts for the Triple-A Express before Monday's recall.
Ranaudo, 25, is 0-1 with a 7.63 ERA in four relief appearances for the Rangers this season. He allowed five runs in three innings in the Rangers' 10-0 loss at Houston on Sunday.