In return for Bryant, the Cubs received two prospects -- outfielder Alexander Canario and right-handed pitcher Caleb Kilian -- from the Giants.
Bryant, who has a .267 batting average with 18 home runs and 51 RBIs this season, immediately provides a boost to the Giants' lineup as San Francisco attempts to hold off the Los Angeles Dodgers in the National League West.
Despite numerous injuries to many of their top players, the Giants lead the division by three games entering Friday's slate. Buster Posey, Brandon Belt, Evan Longoria and Brandon Crawford all have spent time on the injured list this season.
Drafted by the Cubs in 2013, Bryant earned Rookie of the Year and NL MVP honors in consecutive seasons. He helped the Cubs end their 108-year World Series championship drought in 2016.
In seven MLB seasons with the Cubs, Bryant had a .279 batting average with 160 home runs and 465 RBIs. He is one of just three third basemen in franchise history to have multiple seasons with 30 or more homers, joining Aramis Ramirez and Ron Santo.