The Giants selected Brubaker's contract from Triple-A Sacramento on Monday.
Brubaker inked a minor-league deal with San Francisco last month following his release from the Yankees. The 31-year-old right-hander pitched in 12 games out of the bullpen for New York this season, logging a 3.38 ERA, 1.19 WHIP and 10:9 K:BB across 16 innings. He'll likely work in relief for the Giants initially, but he could get a look in the rotation at some point in September with injuries having tested the team's starting depth of late.