Sarkozy has already been charged in two other cases. Here is a summary of the various scandals involving the ex-president directly, or people close to him:
Since 2013, investigating magistrates have been examining allegations that Kadhafi's regime helped finance Sarkozy's successful 2007 presidential campaign.
The first claims were made by the Libyan dictator's son Seif al-Islam in 2011 who said the French rightwinger should "give back the money he took from Libya to finance his electoral campaign."
A year later, the investigative website Mediapart published a document allegedly signed by a Libyan intelligence chief saying that Kadhafi had agreed to support Sarkozy with up to 50 million euros.
Since then, former Libyan spy boss Abdullah al-Senussi, a lawyer to a former prime minister, one of Kadhafi's cousins and a former interpreter have all made allegations about illicit financing.
Documents belonging to former Libyan oil minister Shukri Ghanem, which refer to three payments in 2007, as well as a taped interview with a businessman who claimed he delivered suitcases stuffed with cash for Sarkozy, have added to evidence against the former president.
Former French leader Sarkozy held over Libyan funding inquiry
Sarkozy has denied all the allegations, portraying them as the work of angry members of the former Libyan regime that he helped depose via a NATO-led offensive against Kadhafi in 2011.
Among other leads, investigators have probed a 500,000-euro payment from overseas made to Sarkozy's close aide Claude Gueant in 2008, as well as the sale of a luxury villa for an inflated price in the south of France to a Libyan investor.
This also relates to allegations that Sarkozy's then-UMP party accepted illicit payments for the 2007 campaign, this time from L'Oreal heiress Liliane Bettencourt in the form of cash-filled envelopes.
After a lengthy investigation which he claimed was politically motivated, Sarkozy was personally cleared last year of taking advantage of the elderly woman while she was too frail to understand what she was doing.
But his campaign treasurer is one of 10 people awaiting trial in the case.
Sarkozy has been charged over the illegal funding of his failed 2012 reelection bid which featured huge US-style stadium rallies.
His campaign overshot strict French campaign spending limits by more than 10 million euros through a system of fake invoices which were fraudulently passed off as party expenses.
Sarkozy has denied any knowledge of the alleged fraud.
In February 2017, a judge ordered that the case be brought to trial. Sarkozy and 13 other co-accused have appealed the decision to send the case to trial.
Sarkozy has been charged with corruption and influence peddling over an alleged attempt by his lawyer to get information from a judge who was investigating him.
In recordings from a phone that had been secretly tapped, the lawyer discusses the possibility of giving a magistrate from a top appeals court, Gilbert Azibert, a juicy job in Monaco in return for information on the Bettencourt investigation.
Sarkozy has argued that the job never materialised, meaning he is not guilty of anything, but investigators believe the deal fell through because the former president and his lawyer learned their phones were being tapped.
French ex-leader Nicolas Sarkozy charged with corruption
This long-running investigation involves two former Sarkozy aides who have been charged by judges probing alleged kickbacks on a Pakistani arms deal concluded when Sarkozy was budget minister.
A shell company was allegedly used to channel kickbacks to then prime minister Edouard Balladur's unsuccessful 1995 presidential bid, which Sarkozy helped run.
Sarkozy has been interviewed as a witness, not a suspect, while Balladur faces corruption charges.
Magistrates are also probing whether a 2002 Karachi bombing that killed 11 French engineers was revenge for the cancellation of bribes secretly promised to Pakistani officials.
Six people have been charged over a controversial 400-million-euro payout by the French state to tycoon Bernard Tapie in 2008.
Judges investigated whether the former Adidas owner received favourable treatment in the case as a reward for supporting Sarkozy in the 2007 election.
The case ensnared IMF chief Christine Lagarde, who was found guilty of "negligence" in 2016 for authorising the Tapie payout when she was finance minister, through a private arbitration panel, instead of a court.
Sarkozy has not been targeted personally.
Investigators have charged three former presidential aides for benefiting from contracts for opinion polling carried out during Sarkozy's 2007-12 term as president.
The probe was triggered by anti-graft organisation Anticor, which says the contracts were handed to political cronies without any tender process and public funds were used to carry out political party electoral research.
Sarkozy benefited from legal immunity in the case. The investigation concluded in May 2017.
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