The Brazilian defender has opted for a new challenge after just one year with the Europa League losing finalists
The Brazilian centre-back joined Braga from Naval last summer and played an important role in the club's runner-up finish in the Europa League.
Paulao, who has signed a three-year contract with Saint-Etienne, was offered the opportunity to extend his stay at Braga, but preferred a move to the French club, who finished 10th in Ligue 1 last season.
"I feel honored to have signed for Saint-Etienne, their sporting project has seduced me," Paulao told the club's website.
"The conditions to face the challenge which the French league representatives are met. I am really motivated."
Paulao has become the club's second transfer of the summer, following the loan signing of Sporting Lisbon's Florent Sinama-Pongolle.