Heloisa Helena, 44, formed her own party with other rebels after being kicked out the ruling Workers' Party, PT, in 2003 for voting against the government.
In the last two months she has almost doubled her showing in the polls as the candidate for the Socialism and Liberty Party, PSOL, from 7% to 12%.
In the state of Rio de Janeiro, she is in a technical draw with Luiz Inacio Lula da Silva, the Brazilian president, who is the favourite for the first round on October 2.
With the campaign trail in full swing, Lula and his chief adversary Geraldo Alckmin of the Brazilian Social Democratic party (PSDB), are spending around R$80 million (US$36 million) in slick election propaganda.
In contrast, Helena's tiny PSOL party has a war chest of just R$5 million (US$2.3 million) and its banners are largely hand-painted efforts featuring the party's beaming sun symbol.
But HH, as Helena has become known, has become front-page news with her surge in the polls and stands out as the ethical and moral candidate in a country mired in corruption scandals.
She has never "sold out", she says.
And her popularity is gaining.
On 14 August, HH emerged as the winner of the first televised presidential debate moderated by leading political commentator Ricardo Noblat.
The debate was marked by the absence of presidential candidate Lula, whose refusal to take part was marked by a very visible empty chair.
Noblat later remarked that: "Alckmin was an efficient technocrat as always - and was excessively cerebral and boring. Heloisa was the only one who spoke with emotion which could have woken up the sleeping viewers."
"Democracy always loses when a president of the Republic refuses to submit to criticism"
Paulo Moreira Leite,
blogger for Estado do Sao Paulo newspaper
Paulo Moreira Leite, who writes a blog for the Estado do Sao Paulo newspaper, told Aljazeera.net that Brazil's political process lost out overall due to Lula's absence: "Democracy always loses when a president of the republic refuses to submit to criticism."
However, he added that the president would likely not have lost many votes.
Helena's demeanour and performance at the debates have only reinforced her image as a tough, courageous and honest candidate, according to opinion polls.
But her gains are attributed more to an anti-Lula protest vote than to her own policies, which are seen as extreme left.
"The continuing connection of the PT with neo-liberalism has left a vacuum which needs to be occupied by a new party of the left. More than this we need to stop the PSDB, who favour privatisation, as a top priority. PSOL fulfils this role," states Helena's political literature.
Alckmin is the loser in all this, seeing his numbers in the polls decrease from 29% to 21% in the same period.
Lula has oscillated between 44 and 47%.
Political scientist Paulo de Moura told Aljazeera.net that Alckmin is not winning Brazilian hearts and minds because he has limited himself in the campaign to being viewed as the anti-thesis of Lula.
But "Heloisa Helena's poll numbers have risen because she is efficient in the use of her time in the media and she represents the best anti-Lula and anti-corruption feeling of politics in general".
Helena's political campaign has aligned her strongly with Brazil's landless farmer's movement, the MST.
One of her clearest policy aims is agrarian reform, and to settle one million landless families in four years at a cost of R$4.8 billion (US$2.2 billion) to the national budget.
"Under the constitution, land which is not in use passes for agrarian reform. It's the law, it is not ideological speculation," she says.
When Lula was elected in 2002, there were 60,000 families camped in makeshift straw and black plastic huts.
Official figures now put that at 230,000, many mobilised by the hope that the President, a historical ally of the MST, would put into practice his previous election promise of effecting radical reform. But the plan has stagnated.
Helena has a clear hold on the women's vote but holds anti-abortion views common in the world's largest Catholic country. She was also once involved in a political tiff with a lesbian opponent whom she attacked as having an "atypical sexual life".
But it is Helena's position – and willingness – to tackle corruption in government that has also emerged as a significant factor in boosting her poll numbers.
She has been vociferous throughout the unfolding of the Bloodsuckers congressional scandal which alleges that 69 deputies and 3 senators were involved in a mafia which siphoned kickbacks from funds allocated to municipalities purchasing new ambulances for hospitals.
Helena has made a point of attending every single session of the five-month-long parliamentary investigation led by the Chamber of Deputies' commission on suspicious activities (Comiss?o de Sindicância da Corregedoria da Casa).
While no members of the PSOL party have been involved in the scandal, parliamentarians from every other major party are being investigated for their roles.
'Socialist by conviction'
All this follows the worst corruption scandal in more than a decade, with the PT accused of having been paid US$12,500 in monthly bribes to deputies in allied parties in exchange for support for passing bills.
That episode put paid to the party's president, treasury minister, chief of staff and secretary general among many others.
Helena's campaign aligns her with
the Landless Farmers Movement
As the new face on the scene, Helena is untarnished by high-office scandal or state-governing incompetence.
In Brazil, which has a compulsory voting system, PSOL's principal slogan, which rhymes in Portuguese, says, "Don't vote blank, vote for her!"
"I'm a socialist by conviction," Helena told TV Globo's primetime news programme Jornal Nacional last week.
"I'm in favour of democracy, but democracy is Brazil doesn't exist," she said, in reference to the extreme disparity of wealth in the country.
"I'm absolutely prepared to be president. I'm like all women in Brazil, I don't like lies."