Matteo Salvini said two other regions of northern Italy – Lombardy and Piedmont – could also follow suit, adding that it was time to reduce the powers of the European Union and return to "national and regional sovereignty".
Salvini also said that plans for a coalition of far-right parties including his own at the European Parliament after elections in May were "well advanced".
The coalition "will not be Eurosceptic but will be in favour of a different Europe," he said, adding however that he continues to support an abandonment of the euro. "The euro has massacred our economy," he said.
The planned European Parliament coalition, which would include France's National Front, is united by three points – "exit from the euro, the struggle against immigration and against unemployment", Salvini said.
Asked about the results of a Swiss referendum against immigration, Salvini said he was "overjoyed", even though there are 60,000 Italian workers in Switzerland and future would-be migrants could be affected.
"I am not xenophobic or racist," he said. "Foreigners with the right papers are always welcome."
"Anyone who still judges people based on the colour of their skin in 2014 is a cretin," Salvini added.
Several leading members of his party have been widely condemned for racist insults against Italy's first black government minister, Cecile Kyenge.
Salvini was elected head of the Northern League in December, beating its founder Umberto Bossi whose family has been caught up in a damaging expenses scandal.