Lawyers for Sarkozy and a number of other people who have been charged in connection with the party funding scandal had asked the court to rule inadmissible pivotal medical evidence relating to the health of France's richest woman, Liliane Bettencourt.
Sarkozy was charged in March with accepting envelopes stuffed with cash from the L'Oreal heiress when she was too frail to understand what she was doing, to fund his successful 2007 campaign.
The charges against him are based partly on a medical report which states that Bettencourt, now 90, had suffered from dementia since at least 2006.
Sarkozy's lawyers had challenged the validity of the medical evidence on a procedural point, arguing that the legal-medical expert who wrote the report was a close friend of one of the examining magistrates in charge of the case, and therefore not neutral.
That argument was rejected and the examining magistrates will now have to decide whether to send Sarkozy and 11 others charged with various offences for trial.
That decision is not straightforward as the prosecutor in the case has recommended that the charges against Sarkozy and five others should be dropped because of a lack of compelling evidence against them.
If convicted, Sarkozy faces up to three years in jail, a fine of €375,000 ($480,000), and a five-year ban from public office which would destroy any hope he entertains of making a political comeback.
Separately, Sarkozy is also being investigated over allegations that he accepted up to €50 million ($65 million) cash from former Libyan dictator Muammar Gaddafi for the 2007 campaign.