The 28-year-old was fifth in the Pacific Coast League with a .360 batting average and his .481 on-base percentage ranked second. He had four homers and 20 RBIs in 31 games.
Butler made his major league debut with the Texas Rangers last season, going 4 for 12 in eight games. The Cardinals claimed Butler off waivers last October.
Outfielder Randal Grichuk was optioned to Memphis on Friday. He hit .143 with one RBI in nine games for the Cardinals after being recalled on April 28.