Ramirez knocked in the game's initial run with a first-inning single then added a three-run home run in the third, handing the Brewers a 5-1 lead.
Corey Hart also contributed a three-run homer and Nyjer Morgan provided a two-run pinch-hit single for Milwaukee, which banged out 12 hits in clinching its three-game series.
Gallardo (9-8) handled the Astros on three hits over seven innings, yielding only one run. The right-hander issued one walk and struck out five.
Astros starter Dallas Keuchel (1-4) allowed six walks and was pounded for seven runs on seven hits in a four-inning appearance.
Jordan Schafer homered for Houston, which wrapped up its worst month in franchise history at 3-27.