Mounir Mahjoubi has told Sky News that Russia is behind continued “high level attacks” and its state-sponsored media are the “first source of false information”.
“Let’s be precise on that,” he said.
“We are accusing Russia Today (RT) and Sputnik News (of being) the first source of false information shared about our candidate and all the other symbiotic ways of working with all these fascist organisations or extreme right news organisations.”
Mr Mahjoubi added: “At the same time, during the same period, with the same rhythm, we are the victim, the target of hackers on our servers.
“We have been the targets of multiple attempts of hacking but we succeeded to stop all of them.”
Mr Mahjoubi was talking to Sky News at the headquarters of Mr Macron’s grassroots political movement, En Marche.
Mr Macron, 39, the former chief of staff and economy minister for incumbent French President Francois Hollande, quit the Socialist party last year to launch his own political movement.
Distancing himself from “the establishment” has proved to be a draw.
The former investment banker is now favourite to win the presidency assuming he makes it through to the second round of the two-stage process.
He is pro-Europe, pro the euro, centrist and liberal – stances which Mr Mahjoubi believes make him the target of state-sponsored hacks.
“These ideas of a more open Europe, of a stronger Europe, of a more progressive France, these ideas for certain countries in the world and for certain private organisations are ideas to fight against.” Mr Mahjoubi said.
Staff at En Marche were unable to offer any concrete evidence for the attempted hacks, citing the invisible and anonymous nature of the hacking process.
But they say their party website and donations website have been disabled temporarily, impacting their fundraising.
“The only thing we can say is that half of all the attacks come from Ukraine, but Ukraine is a pass through country, used as a proxy,” Mr Mahjoubi said.
He says the campaign of misinformation is more damaging, illustrating the problem with a chart showing how inaccurate news about his candidate can spread in hours.
Last month, reports circulated online which raised questions about Mr Macron’s sexuality and his connections to the US banking industry.
Mr Macron was eventually forced to address the rumours, insisting he was not gay and not in the pocket of any US banks.
Yet since then, Mr Mahjoubi said the “fake news” and the separate hacks have continued and give an advantage to Mr Macron’s main opponent, far right leader Marine Le Pen.
“Marine Le Pen is our main enemy… Not only her but the ideas of the Front National,” Mr Mahjoubi said.
“She now has the support of new media like Russia Today (RT) and Sputnik and that wasn’t the case before.
“She has the support of the galaxy of people online which we call the social sphere.
“She has the most effective online troops.”
RT and Sputnik, both funded by the Russian state, have strenuously denied ever having published fake news.
“The accusations are false and lack any evidence,” Sputnik said in a statement.
RT added that they “adamantly reject any and all claims that it has any part in spreading fake news in general and in relation to Mr Macron”.
The French government and intelligence agencies have both expressed concern that Russia is attempting to influence the result of the election.
The polls suggest a win for Ms Le Pen is an increasing possibility.
She is anti-EU and has called for a referendum on France’s EU membership within six months.
A Frexit would cause irreconcilable damage to the European Union – a geo-strategic goal for Russian President Vladimir Putin.
Alexandre Melnik is a former Soviet Union diplomat.
He is now a professor of geopolitics in France and no fan of Mr Putin.
“I think this is the global strategy of Russia: through cyber war, through hackers – this is how to kill the fundamentals of western democracy and to take the global leadership of the 21st century.
“Today, the Kalashnikov perhaps is replaced by one click.
“We live in this civilisation of ‘click’ and Putin is aware of that and so he uses, with strong power, hacking and intervening in internal affairs of different countries, through one click.”
The Kremlin has repeatedly laughed off suggestions that it has meddled in either the US or the French elections.
Kremlin spokesman Dmitry Peskov said: “We didn’t have and do not have any intention of interfering in the internal affairs of other countries.
“That there is a hysterical anti-Putin campaign in certain countries is an obvious fact.”