Keuchel, 34, had stints earlier this season with the Chicago White Sox and Arizona before getting released by both teams. The left-hander and two-time All-Star selection was 2-5 with a 7.88 ERA in eight starts with Chicago prior to being designated for assignment. Keuchel was 0-2 with a 9.64 ERA in four starts with the Diamondbacks, his last coming on July 12.
Keuchel was given his outright release by Arizona last week. The Rangers said Keuchel is expected to report to triple-A Round Rock later this week.
Over his 11-year career in the majors, Keuchel is 101-89 with a 3.92 ERA. He was the 2015 Cy Young winner after posting a 20-8 record with Houston.