The former president, who is also embroiled in two other major legal cases, faces accusations that, if true, would become the biggest scandal in France since the end of World War II.
Magistrates have been investigating the Libya allegations since 2013, following claims by investigative website Mediapart that former Libyan leader Moamer Kadhafi had secretly contributed five million euros to his elections campaign, some of it smuggled into France in cash.
Sarkozy's former right-hand man, Claude Guéant, has already been charged with fraud and laundering the proceedings of tax evasion in relation to the same case.
Businessman Alexandre Djouhri, an alleged intermediary between the Kadhafi regime and Sarkozy, was arrested in London and is awaiting possible extradition to France, possibly in July.
Five million euros "transported in cash"
The case against Sarkozy and his lieutenants gathered steam in November 2016, when Franco-Lebanese businessman Ziad Takieddine admitted having transported five million euros in cash between in late 2006 and early 2007.
Further evidence, gathered principally by Mediapart and Le Monde newspaper, includes:
Notebooks by former Libyan prime minister Choukhri Ghanem mention the deal - Ghanem, who fled to Vienna after the Libyan civil war erupted, was found floating in the Danube in 2012, his death being described as accidental by Austrian investigators but considered "highly suspicious" by the US secret services;
In testimony kept under wraps for some time, Kadhafi's secret service chief Abdallah Senussi told the International Criminal Court that he had supervised the transfer of the money via Guéant and Takieddine;
An official document signed by then external secret service chief Moussa Koussa in 2006 informs the head of Libya's sovereign fund, Bashir Saleh Bashir, of the agreement - Sarkozy-era secret service chief Bernard Squarcini allegedly helped Bashir flee France for Niger and then South Africa, where he was the subject of an assassination attempt in February this year;
Claude Guéant, whom investigators observed made "immoderate use of cash" for personal transactions, rented a huge safe in a Paris bank during the election campaign - he told investigators he stocked copies Sarkozy's speeches in it;
Before his death, Kadhafi himself referred to a "serious secret" about his relations with the West as war erupted in his country and his son, Saif al-Islam, who is currently under house arrest, has mentioned the alleged financing.
Sarkozy has consistently denied the accusations, describing them as "slanders".