Reliever David Goforth was optioned to Triple-A to make room for Gennett on Thursday.
Gennett spent more than three weeks in the minors after hitting just .154 in 21 games in Milwaukee. It was a disappointing start for the left-handed hitter, who began the year as the starter after former platoon partner Rickie Weeks was let go in the offseason.
Gennett hit .307 with two homers and 11 RBIs in 17 games at Colorado Springs.
The Brewers did get a fresh arm back for Thursday's game against Washington with left-hander Will Smith returning from a six-game suspension for being found with a foreign substance on his right arm.