Pomeranz, 30, is 2-9 with a 5.68 ERA in 21 games (17 starts) this season. Pomeranz has struggled the last two seasons after going 17-6 with a 3.32 ERA in 32 starts for the Boston Red Sox in 2017.
Milwaukee will also receive relief pitcher Ray Black, who has a 4.50 ERA in two games this year. Black was 2-2 with a 6.17 ERA in 26 games for the Giants last season.
Pomeranz is 46-57 with a 4.09 ERA since debuting with the Colorado Rockies in 2011.
The Brewers and Giants are separated by only 1 1/2 games in the NL Wild Card race. Milwaukee is 56-52 and one game behind the Chicago Cubs and Philadelphia Phillies for the National League's second Wild Card spot.