The rightwing Fillon, who polls show is likely to reach the runoff of the election in May, is facing an investigation into claims he gave his British-born wife Penelope a fictitious paid role as a parliamentary aide.
With the allegations dominating coverage of the campaign, Fillon's lawyer Antonin Levy met with investigators and handed over several documents.
"I had a meeting with (investigating) magistrates from the national financial prosecutor and gave them the documents," Levy said.
"We agreed to talk again as often as is necessary," he added.
Fillon is to appear on France's main evening news show on TF1 at 1900 GMT.
His campaign manager, senator Bruno Retailleau, predicted earlier that the scandal would be short-lived.
"I tell you, this thing is going to fizzle out very quickly," he said.
Polls currently show that Fillon will face far-right candidate Marine Le Pen in the second round of the election, although centrist candidate Emmanuel Macron is rising fast in the polls.
'Clean' candidate
The allegations are potentially damaging to the 62-year-old, who owed some of his surprise victory in the rightwing primary contest to a "clean" image.
In the early debates, he contrasted his record with that of former president Nicolas Sarkozy's legal woes, saying: "It's hard to imagine General de Gaulle being prosecuted."
The claims about his Welsh-born wife first surfaced in the Canard Enchaine weekly, which mixes satire and investigative reporting.
The paper said it had been unable to find anyone who remembered Penelope working in parliament.
Fillon has dismissed the allegations as "mudslinging" and "misogynistic".
In a statement later Wednesday, Fillon said he hoped to speak to investigators "as soon as possible (to) set out the truth", adding that the claims were "baseless".
Fillon's spokesman Thierry Solere confirmed to AFP on Tuesday that Penelope had worked for her husband and said the arrangement was "common" among French MPs.
Hiring family members is not against French parliamentary rules if the person is genuinely employed, but attention is focused on precisely what work Penelope carried out for a salary of sometimes around 7,000 euros a month.
The Canard Enchaine alleged that Penelope received the money between 1998 and 2012.
It said she also worked for a periodical, Revue des Deux Mondes, owned by a friend of Francois Fillon, between May 2012 and December 2013.
The silver-haired mother-of-five has kept a low profile in Fillon's nearly four-decade political career, telling a newspaper during the rightwing primary campaign last year: "Until now, I have never got involved in my husband's political life."
The couple, who met in their early twenties when she was studying in France, live in a chateau near Le Mans in the northwest.
