Varejao cleared waivers Sunday and will earn the veterans minimum with Golden State for the remainder of the season, sources told ESPN's Marc Stein.
The Warriors, who own the NBA's best record at 49-5, were competing with the rival Spurs for Varejao, who spent his first 11-plus seasons with Cleveland.
Varejao, 33, appeared in 31 games this season for the Eastern Conference-leading Cavs, averaging 2.6 points and 2.9 rebounds per game. But the 6-foot-10 Brazilian will add much-needed size to the Warriors, who are short-handed along their front line because of injuries.
On Monday, Golden State released forward Jason Thompson, creating an open roster spot.
Varejao was dealt to Portland on Thursday before the trade deadline as part of a three-team swap that landed Channing Frye with the Cavaliers. The Blazers promptly agreed to waive Varejao despite the two years and nearly $14 million in guaranteed money left on his contract after this season.
ESPN's Marc Stein contributed to this report.