"I have not misappropriated public funds… I have trusted the people close to me with jobs… because I knew I could count on their trust and their competence," Fillon said at the press conference.
Fillon blasted the ongoing judicial inquiry as an attempt of "political assassination" directed at him. Having pleaded not guilty in the case of employment of his family members, Fillon will now have to prove it in court.
"I won't give in, I won't surrender, I won't pull out, I'll fight to the end," Fillon said ending his speech.
Earlier, French media reported that Fillon's presidential campaign director Patrick Stefanini had offered his resignation. There has been no confirmation yet.
The French financial prosecutor's office launched an official investigation on February, 24 into an allegedly fake employment of Fillon's wife. The investigation is devoted to assignment of state funds, complicity, concealment of offenses and trading in influence.
French presidential elections are due to take place in two rounds on April 23 and May 7.