Miller was released by the Texas Rangers last week after the team had designated him for assignment.
Looking to bounce back after a series of injuries, Miller signed a one-year, $2 million deal with the Rangers in the offseason, but he struggled mightily with the team before being designated. In 19 appearances, including eight starts, he was 1-3 with a 8.59 ERA. Opponents were hitting .317 against him.
Prior to this season, the 28-year-old Miller had thrown a total of just 139 innings since the start of 2016, going 5-18 with a 6.35 ERA, as he dealt with several injuries, including Tommy John surgery.
Milwaukee comes out of the All-Star break at 47-44, a half-game behind the National League Central-leading Chicago Cubs.