Dilma Rousseff was the president's own choice
The governing Workers' Party in Brazil has endorsed the president's chief of staff as its candidate for presidential elections in October.
Economist Dilma Rousseff was personally nominated by President Luiz Inacio Lula da Silva, who is prevented by law from standing for a third consecutive term.
She promised fiscal discipline and economic stability if elected.
But correspondents say she faces tough competition from the conservative opposition.
After the endorsement was announced, she said: "I humbly receive this mission that you are giving to me.
"[I receive it] with humility, but also with courage and determination. Courage and determination which come from the support that I receive from my party and from its most distinguished member, President Lula."
Under electoral law, Ms Rousseff must step down from her current post by 3 April, six months before the election.
She said she wants to form a coalition government, and would continue working with President Lula's current coalition of 11 parties.