Dilma Rousseff is Lula's preferred choice to succeed him
The campaign to succeed Brazilian President Luiz Inacio Lula da Silva has begun in earnest, with the two front-runners leaving their current jobs.
Dilma Rousseff, Lula's chief of staff, stepped down while Sao Paulo Governor Jose Serra also resigned.
They needed to meet a 2 April deadline to be able to run in October's poll.
Central Bank Governor Henrique Meirelles is expected to announce soon whether he is resigning in order to run for political office.
Mr Meirelles is the longest-serving Central Bank governor in Brazilian history and credited with helping to steer Brazil through the global economic crisis.
Jose Serra has been a fixture in Brazilian national politics for years
Earlier in the week, Mr Meirelles said President Lula had asked him to remain in the post until the end of the year.
He had been reported to be considering a run for a Senate seat or even a bid to stand as vice-presidential candidate on Ms Rousseff's ticket.
On Wednesday, Ms Rousseff and nine other members of the cabinet, as expected, stepped down from their posts to become eligible to run for elected office in October.
"We leave not saying a farewell but a 'See you soon'," Ms Rousseff said.
Ms Rousseff, Lula's choice to succeed him, was endorsed last month by the Workers Party (PT) as its candidate.
President Lula is prevented by law from standing for a third consecutive term.
Also on Wednesday, Mr Serra, of the Brazilian Social Democratic Party (PSDB) delivered a speech on his three years as governor of Brazil's most populous state.
He said he was leaving "satisfied with what he had achieved".
The official launch of Mr Serra's candidacy is set for 10 April.