Brazilian President Luiz Inacio Lula da Silva is to stand for re-election in presidential elections due in October.
President Lula's popularity plummeted last year
The president announced his decision to seek a second term at the national convention of his Workers' Party.
He became the first leftwing contender to hold office in nearly half a century in a landslide victory in 2002.
Opinion polls suggest his popularity is on the up after a corruption scandal engulfed party members and tarnished the image of his party last year.
The scandal over campaign funding and alleged bribes for votes in congress led to the resignation of the party leader and several high-level colleagues.
But the BBC's Simon Watts says the president's down-to-earth personality has stood him in good stead, with working-class voters generally believing that he was let down by his aides.
"I'm here to tell you once more that I've accepted, from the bottom of my heart, the call ...to continue the struggle for a more just and independent Brazil, where each Brazilian can eat three times a day, can have a job, education and good health," Lula, 60, told a crowd of some 2,000 party delegates.
A stable and growing economy has also helped to increase Lula's popularity, our correspondent says, as well as a programme which guarantees millions of poor Brazilians a basic income.