Brazil's Socialist party (PSB) has named popular environmentalist Marina Silva as its presidential candidate, reshaping the political landscape after her running mate Eduardo Campos died in a plane crash.
Campos' death has transformed the outlook for the October vote, possibly setting up Silva, his former vice-presidential candidate, to unseat incumbent Dilma Rousseff in a run-off, according to the latest poll.
"I will give the best I have in me," said Silva, 56, a former environment minister, after the announcement on Wednesday.
"Our proposals seek a more just, economically prosperous and socially fair, politically democratic and environmentally sustainable Brazil," added Silva, whose life story is one of astounding personal mobility.
Born into a poor family of rubber tappers in the Amazon, she only learned to read and write at 16, the start of a meteoric rise to become a leader of the country's environmental movement.
The PSB party president, Roberto Amaral, said Silva was chosen unanimously to replace Campos at the top of the ticket.
"We had the immense luck to have her as a substitute," he said.
Socialist legislator Beto Albuquerque was named the as vice-presidential candidate.
The PSB had been widely expected to name Silva after Campos, 49 and a former governor, was killed when his campaign jet crashed when travelling to Sao Paulo.
Before Campos' death, the election outlook had been stable for months, with Rousseff polling about 36 per cent, Social Democrat candidate Aecio Neves 20 per cent and Campos 8 per cent.
But Silva's entry into the race could prove a real threat for Rousseff, who is seeking a second four-year term.
On Monday, polling firm Datafolha put Silva in second place ahead of the October 5 first-round vote, with 21 per cent support against 36 per cent for Rousseff and 20 per cent for Neves.
And it found she would beat Rousseff in an October 26 run-off, 47 per cent to 43 per cent.
The poll was the first taken since Campos' death in the August 13 crash.
Silva has been considered a top contender since surprising many pundits in the 2010 election by coming in third with 19 per cent of the vote running on the tiny Green Party's ticket.
But Brazil's electoral court ruled last October that she had failed to collect enough signatures to register her new party, Sustainability Network, in time for this year's race.
She then opted to join forces with Campos and the PSB. As an evangelical Christian, she appeals to both religious conservatives and also the left.