The 32-year-old was a free agent after being released by Marseille at the end of last season.
"Everyone knows the qualities of Brandao," St Etienne chief executive Roland Romeyer told the club's official website.
"He is a player who works hard, a warrior who does not shrink from the fight.
"Throughout his career he has scored important goals. I remember his goal against Lyon last season in the final of the Coupe de la Ligue and one against Inter Milan which helped OM reach the quarter-finals of the Champions League.
"His record speaks for itself, he's a competitor."
Brandao spent three years at Marseille, winning the Ligue 1 title in 2010, after a seven-year stint with Ukrainian giants Shakhtar Donetsk.