Fillon, a conservative who was once frontrunner, has been battered by a stream of revelations since late January, focused on parliamentary jobs given to his wife and his links to a billionaire businessman.
Investigating magistrates charged Fillon on Tuesday, a day earlier than expected, with misuse of public money, misuse of corporate assets, and failing to declare his assets to a public watchdog, legal sources told AFP.
"The hearing was brought forward so that it could take place in a calm manner," lawyer Antonin Levy told AFP.
Fillon's Welsh-born wife Penelope was paid hundreds of thousands of euros from public funds between 1986 and 2013, but she is accused of doing little work for the salary.
From May 2012 to December 2013, while employed by Fillon's parliamentary office, she was on the payroll of a magazine owned by tycoon Marc Ladreit de Lacharriere, who also gave Fillon an undeclared loan.
Macron trip probed
Fillon's problems have benefited centrist independent Emmanuel Macron in particular, as well as far-right leader Marine Le Pen, who are shown in opinion polls as the likely top two candidates in the first round of voting on April 23.
Polls suggest 39-year-old Macron would beat Le Pen in a decisive run-off on May 7 -- but after Donald Trump's victory in the United States and Britain's vote to leave the European Union, analysts caution against bold predictions.
Macron's campaign was buffeted Tuesday by news that the Paris prosecutors' office had opened a probe into the organisation of a 2016 event for hi-tech French companies in Las Vegas financed by the economy ministry which he headed at the time.
Prosecutors are looking into whether there was favouritism in selecting PR firm Havas to organise the evening costing nearly 400,000 euros ($425,000) without a public tender -- at which Macron was the star speaker.
The candidate, head of his new "En Marche" (On the Move) movement, is not targeted personally at this stage and denies any wrongdoing.
Le Pen also faces multiple investigations over campaign financing and misuse of money at the European Parliament.
Two aides, including her personal assistant, have been charged but she has refused to reply to summons from judges over the parliamentary expenses case.
Following reports in the Canard Enchaine newspaper at the end of January, Fillon admitted to employing Penelope and two of their children as parliamentary assistants.
After initially saying he would withdraw from the presidential race if charged, Fillon has vowed to continue, calling the investigation an attempted "political assassination".
Speaking to French media on Tuesday, he repeated his assertion that the investigation was designed to discredit him, saying that the judicial calendar seemed to be "coordinated with the political campaign."
The prime minister from 2007-2012 was the surprise winner of the Republicans' primary in November after campaigning as a clean and honest candidate who would transform France with a "radical" economic programme.
He wants to slash public spending by 100 billion euros ($106 billion) and cut 500,000 public sector jobs over the next five years.
Rebels in his party have now accepted that attempts to dislodge him have failed ahead of a deadline for presidential candidates this Friday, but a constant drip of revelations continues to undermine his campaign.
Le Parisien newspaper reported new details on Tuesday about how two of his five children, Charles and Marie, turned over part of their parliamentary salaries to their parents.
Of the 46,000 euros paid to Marie between October 2005 and December 2006, she transferred 33,000 euros into her parents' joint bank account, the paper said.
Her lawyer said the money was to reimburse her parents for her wedding.
At the weekend, the Journal du Dimanche said Fillon had been gifted clothing worth nearly 48,500 euros ($51,800) furnished by jet-set tailor Arnys since 2012.
It is the first time a candidate of a major party will seek the keys to the Elysee Palace with such major legal problems.
Ex-president Jacques Chirac was found guilty in 2011 after leaving office over a "fake jobs" scandal while he was mayor of Paris in the 1990s.
Former president Nicolas Sarkozy, leader while Fillon was prime minister, is under investigation on charges of illegal campaign financing among others.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)