The Brewers confirmed the signing on their official Twitter account after team owner Mark Attanasio said at a fan event Sunday a four-year deal with Garza had been struck.
The contract needs final approval from Major League Baseball and the players association, Attanasio said.
Terms of the deal with the 30-year-old right-hander weren't announced, but reports indicated the two sides had agreed to $52 million. Garza was the top pitcher remaining in the free agent market after the New York Yankees inked Masahiro Tanaka Wednesday.
Garza compiled an 10-6 record with a 3.82 ERA and 136 strikeouts over 155 1/3 innings in 24 combined starts between the Chicago Cubs and Texas Rangers last season.
He sports a 67-67 lifetime record and a 3.84 ERA over eight seasons with the Minnesota Twins, Tampa Bay Rays, the Cubs and Rangers.