The title announced Wednesday went to Mangueira, which is one of the oldest and most traditional samba schools.
The group's theme was Brazil's unsung heroes, including councilwoman Marielle Franco, who was shot to death a year ago. Her killing set off a wave of demonstrations, but police are yet to name suspects.
Several flags with Franco's face in Mangueira's colors of green and pink appeared in its parade early Tuesday and also on Wednesday as the Carnival jury announced the winner.
Progressives hail the black, shantytown-born politician for activism for the LGBT community, while supporters of far-right President Jair Bolsonaro often reject her as a symbol.