The president of the Workers’ Party, Senator Gleisi Hoffmann, told journalists that Mr. da Silva had not given up on his quest to return to the presidency. “Lula remains our candidate, first of all because he is innocent,” she said. “If he is jailed, we will consider him a political prisoner and we will be by his side.”

Mr. da Silva, 72, kept a low profile on Thursday, receiving a string of visitors in his office at the Lula Institute in São Paulo, including party leaders and his handpicked successor, former President Dilma Rousseff.

While Mr. da Silva is not the first Brazilian leader engulfed in scandal — former President Fernando Collor de Mello stepped down to avoid being impeached in 1992 and Ms. Rousseff was impeached on charges of manipulating the budget to hide economic problems — his fall is striking nonetheless. He left office eight years ago with a record approval rating of 87 percent, and he has held an ample lead in polls for October’s presidential election.

Mr. da Silva’s imminent imprisonment also sends a chilling message to other prominent political figures caught up in corruption investigations. The threat of jail time has been one of the most important tools in the large-scale investigation known as Lava Jato, or Car Wash, which has ensnared not only Mr. da Silva, but also dozens of business and political leaders, including President Michel Temer.

Last July, Mr. da Silva was convicted on corruption and money laundering charges and sentenced to almost 10 years in prison. In January, an appeals court unanimously upheld the conviction and increased the sentence to 12 years. Mr. da Silva maintains that the prosecution was an underhanded ploy masterminded by rivals to keep him off the ballot.