The Brazilian striker scored after 20 minutes to decide an exciting game in Paris, giving Christophe Galtier's men the first major silverware of the French season
A goal from Brandao midway through the first half was sufficient to separate the sides in what was a high-paced encounter that did not want for excitement.
Champions League chasing Sainte dominated much of the game and were rewarded on 20 minutes when they took the lead. Pressing high up the field, Renaud Cohade robbed the ball from the Bretons before Yohan Mollo slipped a neat pass down the left channel for Pierre-Emerick Aubameyang, whose wonderful centre picked out Brandao. From inside the six-yard box the Brazilian striker could not miss the empty net with his left foot.
A late volley from Sadio Diallo nearly squared the match but Stephane Ruffier saved Christophe Galtier's side with a fine diving stop to his left.
For a period after they opened the scoring les Verts threatened to blast Rennes away as Fabien Lemoine sent a fizzing shot a foot too high before Aubameyang again cross for Brandao, who was this time expertly denied by Benoit Costil in the Rennes goal.
The first half of the game had started in a thrilling manner, with Mevlut Erding drawing a good save from Saint-Etienne goalkeeper Stephane Ruffier within 30 seconds before Francois Clerc shot just wide at the other end.
The beginning to the second period was similarly promising but after Yohan Mollo’s foray down the left, Cohade failed to find the target from the cutback. Shortly afterwards a Clerc header from another corner was cleared from the line by Jonathan Pitroipa.
Rennes’ offensive talisman was awoken by this moment and started to dictate play more at the other end of the field.
Nevertheless, it was substitute centre-back John Boye who had the Bretons’ best chances to find a leveller. The Ghanaian steered a header just wide following a hopeful long ball into the box before again showing his aerial power from a corner kick, though his effort was not steered sufficiently away from Ruffier to test the goalkeeper.
The shot-stopper, however, did brilliantly to thwart Diallo with four minutes left and secure a long-awaited title, much to the delight of their army of fans that bedecked Stade de France in green, not to mention a huge watching public back in Loire.
Now with European football secured for next season, they can focus on a top-three finish in Ligue 1 and a potential Champions League adventure.