Umberto Bossi, the founder of the Northern League Party and a former ally of ex-premier Silvio Berlusconi, resigned today amid a scandal concerning allegations of misuse of party funds.
Bossi presented his "irrevocable resignation" as the anti-immigration party's general secretary during a party meeting in Milan, Italian media said.
He was immediately appointed to the honorary post of president.
The outspoken Bossi -- the figurehead for the League party, which frequently criticises government corruption -- is implicated along with his family members and associates in a scandal over the use of public funds managed by the party.
The high-profile fraud inquiry has centred on the party's treasurer, Francesco Belsito, who resigned from his post on Tuesday. Prosecutors are also looking into possible links with organised crime and money laundering.
One part of the probe is focused on investments of five million euros ($6.7 million) in Cyprus and Tanzania allegedly made by Belsito.
Belsito and his associates are also alleged to have used taxpayers' money to refurbish Bossi's house and pay for travel and accommodation for his children.
Bossi -- who presented himself as a refreshing political alternative during corruption scandals in Italy in the 1990s -- denied any knowledge of the fraud.
His position will be temporarily filled by ex-ministers Roberto Calderoli and Roberto Maroni, as well as League member Manuela Dal Lago.
"Now we are going to do some housekeeping, we're going to look at the accounts and search in all the cupboards," Maroni told ANSA news agency.
The case is being investigated by prosecutors in Milan, Reggio Calabria and Naples, where organised crime groups are suspected of having helped launder money held by the League.
The Northern League rose to prominence in the early 1990s with a separatist, Eurosceptic and anti-immigration platform and brought down Berlusconi's first government in 1994 by withdrawing from his coalition.
The scandal comes at a difficult time for the party, which is considered a plaintiff in the investigation.
It is the only party in parliament opposed to Prime Minister Mario Monti, and the other main parties may now stand to win votes if disaffected League followers withdraw their support in the upcoming local elections in May.