The Sunday vote in Congress could topple the 68-year-old leftist leader, in a political crisis threatening to destabilize Latin America's biggest economy as it struggles through a crippling recession.
It will be a rare outing for Rousseff, who has preferred to remain at her official workplace, the Palacio do Planalto, encouraging supporters from afar.
Rousseff will meet with the supporters camped out at the Mane Garrincha stadium who have turned out to support her bid to remain head of state.
"We came to join the defense of democracy and the government that was legitimately elected in 2014," said Tiago Almeida, 35, a metal worker from the state of Sao Paulo who has been at the camp for days.
Organizers hope that more than 100,000 will gather at the rally and the support camp this weekend.