Catcher Erik Kratz will back up Buster Posey in San Francisco after the Giants traded for the veteran on Sunday.
The Giants sent minor league infielder C.J. Hinojosa to the Milwaukee Brewers in exchange for Kratz.
Kratz, 38, agreed to a one-year deal worth $1.2 million, with $300,000 guaranteed, with the Brewers in November.
Milwaukee added Kratz last May in a deal with the New York Yankees and he played in 67 games for the Brewers, batting .236 with six home runs and 23 RBIs.
He caught fire in the National League Division Series against the Colorado Rockies, collecting five hits in eight at-bats. He cooled off in the NLCS loss to the Los Angeles Dodgers, finishing with two hits in 16 at-bats in the seven-game series.
Manny Pina won the backup job in Milwaukee, making Kratz expendable. The Brewers signed reliever Alex Wilson to fill the vacant roster spot.
Kratz made his MLB debut at age 30 with the Pittsburgh Pirates. The 67 games he appeared in last season were the most since 2013, when he played in 68 games with the Philadelphia Phillies.
Hinojosa, 24, has experience at second, shortstop and third base. He spent the bulk of last season at Double-A Richmond, where he batted .261 with three home runs and 26 RBIs in 67 games.