Sarkozy's conservative party, prosecutors said, spent nearly double the 22.5 million euros (currently $19.2 million) allowed under electoral law on extravagant campaign rallies and then hired a friendly public relations agency to hide the cost.
Sarkozy has denied wrongdoing. He said he was not involved in the logistics of his campaign for a second term as president or in how money was spent during the election run-up.
"Can you imagine me going into a meeting to discuss the cost of flags?" he told the court in June. "I had too much to do."
"From the moment I was told things were in order, I had no reason to give it more thought."
But the court said Sarkozy was made aware of the overspending, that he did not act on it, and that it was not necessary for him to approve each individual spending to be responsible.
Several others who face charges were found guilty of fraud over the campaign financing and sentenced to up to 3-1/2 years in jail and hefty fines.
Sarkozy was found guilty in a separate trial in March of trying to bribe a judge and peddle influence in order to obtain confidential information on a judicial inquiry. He also denied any wrongdoing in that case.
The former president was sentenced to three years in jail in that trial - two of which were suspended - but has not spent time in prison yet, while his appeal is pending.
The son of a Hungarian immigrant father, Sarkozy debuted in politics as mayor of the wealthy district of Neuilly outside central Paris, before serving as president Jacques Chirac's finance minister.
As president, Sarkozy's high-energy style and abrasive manner polarised voters. His modest attempts at tax and labour reforms and limited success in creating jobs disenchanted both free-marketeers and centrist voters.
Outside France, he brokered a ceasefire to the Russia-Georgia war in 2008, and in 2011 championed a NATO-led military intervention in Libya to support an uprising against its autocratic leader, Muammar Gaddafi.