The tomorrow 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.
Organisers hope that more than 100,000 will gather at the rally and the support camp this weekend.
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Rousseff's opponents also plan rallies over the weekend as lawmakers debate a motion to send her to an impeachment trial in the Senate.
Police tightly guarded the area around Congress, which was surrounded with metal barriers.
Pro- and anti-Rousseff rallies are also planned in other cities tomorrow, including the economic capital Sao Paulo and Rio de Janeiro, where the Summer Olympics will be held in August.
Rousseff faces charges that she illegally used creative accounting to mask government shortfalls during her 2014 reelection.
She accepts the claims, defending her behavior by saying that previous governments used similar measures.
In a rowdy opening session yesterday, the government's top lawyer Jose Eduardo Cardozo drew noisy complaints when he repeated Rousseff's claim that the impeachment drive was a "coup."
"This is a historic process, there's no doubt," said House Speaker Eduardo Cunha, one of the leaders of the push to remove Rousseff.