The American League champion Rangers hired Maddux away from the Chicago Cubs, where he had held a similar position for two years under since-fired GM Jim Hendry.
Maddux, 45, a four-time Cy Young Award winner, will be reunited with his brother Mike in Texas, where the latter is the pitching coach under Manager Ron Washington.
"We're excited to add Greg to our group and look forward to him contributing to the development of our young pitchers," Rangers General Manager Jon Daniels said.
Greg Maddux will be an instructor for both the minor and major league staffs during spring training. He will also work with the Rangers' farm clubs during the regular season, Daniels indicated.