In the tense run-up to the announcement, Lula told supporters Tuesday that he would continue his political fight regardless of the outcome.
Thousands of people rallied in support of the 72-year former leftist president in the southern city of Porto Alegre, where an appeals court is set to rule on his conviction today.
Hugely popular during his two-term presidency from 2001 to 2010, Lula was sentenced in July to nine and a half years behind bars after being convicted of corruption in Brazil's huge "Car Wash" graft scandal.
"Only one thing will take me off the streets of this country, and it will be the day of my death," Lula told cheering supporters, many wearing the red T-shirts of his Workers' Party (PT).
More From This Section
"Until that moment, I will fight for a more just society. Whatever the outcome of the trial, I will continue fighting for the dignity of the people of this country."
"I am not going to speak today about my trial or about justice, because I have competent lawyers who have proven my innocence," he said.
"I come here to talk about Brazil," added Lula.
"I have the peace of the innocent, of those who did not commit any crime. Are they afraid of me coming back? They are afraid of the good things we did," he said, referring to his right-wing opponents.
Lula, Rousseff and leftist leaders say they are the victims of a plot by the judicial, political and business sectors to sideline the PT.
Helicopters will overfly the courthouse and even ships are being used to protect the building, located adjacent to a river.
Lula will follow the ruling from his home in Sao Paulo.
Rousseff had earlier denounced what she called the "third stage of the coup" against Lula.