Pomeranz is guaranteed to make $1.5 million and can earn up to $5 million with incentives, a source told The Athletic's Ken Rosenthal.
Farhan Zaidi, the Giants' president of baseball operations, was also part of the Oakland Athletics' front office that acquired Pomeranz before the 2014 season.
While his role hasn't been specified, Pomeranz could slot into a Giants rotation already consisting of Madison Bumgarner, Jeff Samardzija, Dereck Rodriguez, and the recently re-signed Derek Holland. Johnny Cueto is unlikely to pitch in 2019 after undergoing Tommy John surgery.
After winning 17 games for the Red Sox in 2017, the 30-year-old Pomeranz posted a 2-6 record with a 6.08 ERA in 26 appearances in 2018. He dealt with several injuries last season, including a strained flexor tendon, biceps tendinitis, and neck discomfort.
Over eight major-league seasons, Pomeranz has been a starter and reliever while logging 710 innings. He owns a 44-48 record with a 3.92 ERA and a 1.35 WHIP.