The Rangers said Tuesday that Wells' retirement was effectively immediately.
In 98 career games in the majors from 2008-12, all but one with the Cubs, Wells was 28-32 with a 4.08 ERA. He was 1-2 in 12 games last season for Chicago, but became a free agent after refusing a minor league assignment.
The 30-year-old Wells went to spring training with the Rangers as a non-roster invitee. The right-hander was 0-4 with a 6.08 ERA for Round Rock.
Rangers general manager Jon Daniels says Wells indicated he "just didn't have the same level of desire" to pitch any more.