"We will not stop until independence," Salvini, who is a lawmaker in the European Parliament, told a party congress in Turin which confirmed his election victory last week against the party's founder Umberto Bossi.
Salvini said his party was preparing unspecified acts of civil disobedience and he looked ahead to European Parliament elections in May saying: "If we have a boom, it will be the beginning of the end of the empire".
Marine Le Pen, the leader of the National Front in France, sent a message of support for Salvini, who has said he is looking forward to working with her.
Salvini is a member of the Europe of Freedom and Democracy Group in the European Parliament along with the United Kingdom Independence Party (UKIP).
The Northern League has been in government three times over the past 20 years as a coalition partner with Silvio Berlusconi but the party has been rocked by a scandal over the misuse of public funds by its leaders.
At the height of its success, the party gained 10 percent of the national vote. In February's general election, however, it won just four percent.