A judicial source said Sarkozy, leader of the centre-right opposition Republicans, had been notified in advance that the summons could lead to his being placed under formal examination, which would be a prelude to a possible trial.
He was driven to the headquarters of the Paris financial prosecutors' office to be questioned about the so-called Bygmalion affair.
Sarkozy has repeatedly denied knowledge of dual accounting and some 18 million euros ($20.1 million) in false invoices issued by the Bygmalion event-organization company that meant his campaign costs were more than double the legal limit.
Four senior figures in the 2012 campaign have already been placed under formal investigation for alleged political financing offences, including his campaign manager and treasurer, Reuters reported.
In a book published last month, Sarkozy wrote: "It will no doubt be hard to believe, but I swear it is the strict truth: I knew nothing about this company until the scandal broke."
The magistrates have the option of placing Sarkozy under investigation or declaring him to be simply a witness in the case, as they did with former party leader Jean-Francois Cope last week.