A judicial source said Mr 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.
Mr Sarkozy has denied knowledge of dual accounting and some €18m in false invoices issued by the Bygmalion event-organisation 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.
In a book published last month, Mr 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 Mr Sarkozy under investigation or declaring him to be a witness in the case, as they did with former party leader Jean-Francois Cope last week.
Several employees at Bygmalion, including the company’s accountant as well as a leading member of Mr Sarkozy’s campaign team, have admitted to the existence of the fraud, though none have accused the former president of knowing about it.
Mr Sarkozy, 61, who led France from 2007 before losing to Socialist Francois Hollande in 2012, said he was retiring from politics after the election but made a comeback two years later, returning to lead the Republicans and lining himself up for party primaries this autumn in a bid to contest the presidential election in May 2017.