The Spanish Supreme Court ruled that the 50-year-old and his team need to pay the amount they guaranteed in the 2002-03 season, during which the club incurred a loss of €60m (£52m).
"It is a clear sentence and the decision is unquestionable," ESPN quotes Barcelona spokesman Toni Freixa as saying.
"It clarifies for once and for all the mandate of the previous board. We expect that we will receive the guarantee because we live in a society which respects the law.
"The sentence orders the accused to guarantee the debt - not to pay it off. We are waiting for the club member who made the original charges to ask for the sentence to be carried out."
Under Spanish law, the ruling can be enforced only if Barcelona member Vicenc Pla, who initiated the case in 2010, decides to do so.
"We have not yet decided," Pla told Catalunya Radio. "The sentence is in our favour, and in favour of the club.
"[But] if they knew they had an obligation to cover the guarantee, why do they not do it?"
However, Laporta believes that it is Barcelona and not Pla who conceived the idea of launching a legal case against him.
"They are the ones who have made the claims," he said. "They are hiding behind Vicenc Pla and want to discredit our good management. It is shameful."
Laporta was the Barcelona president between 2003 and 2010.