“It is time to move forward, it is time to make more changes,” 66-year-old Rousseff told members of her leftist Workers Party (PT) during a convention in Brasilia on Saturday.
The Workers Party approved her candidacy at the meeting, with the popular ex-president Luiz Inacio Lula da Silva on hand.
She remains ahead of her rivals Social Democratic Senator Aecio Neves and socialist ex-governor Eduardo Campos in a recent poll.
Rousseff’s party promises changes in a new administration as protests continued over the handling of the World Cup tournament which began June 12 and ends July 13.
Brazilians have held massive demonstrations since last year's Confederations Cup, which is a prelude to the main football event. The protests are against the World Cup’s enormous USD 11 billion bill and poor public services.
Critics say the money should rather be invested in health, education, transportation, and housing sectors. They also accuse the Brazilian government of corruption in deals related to the infrastructures of the games.