With one-third of the Italian vote, the League is poised to become one of the biggest parties in the European Parliament with 28 seats, according to provisional results. Meanwhile, Salvini's coalition partner in Italy, the populist 5-Star Movement, got only 17 percent, shifting the balance of power from last year's Italian election.
Salvini said before the European vote that a strong result for his party wouldn't change the coalition agreement, but it strengthens his hand in negotiations over government policies that intensified during the election campaign.
"The allies in our government are my friends and from tomorrow we have to go back and work with serenity, lowering the tone," Salvini told reporters as the results were coming in. His party's backing has doubled since the national election a little over a year ago and increased exponentially since the last European election, when it got just 6 percent.
It remains to be seen how Salvini, 46, will capitalize on the momentum. He could demand a reshuffle of the Cabinet or even new elections — or just use his leverage to put more focus on his ambitions to curb illegal immigration and introduce a flat tax in Italy.
The left-wing opposition Democratic Party, which overtook the 5-Star Movement with 24 percent of the vote, suggested the result would lead to a stalemate in the government. "The challenge is to create an alternative to Matteo Salvini who without doubt comes out of these elections as the true leader of a motionless and dangerous government," Democratic Party leader Nicola Zingaretti said.
While the European election outcome doesn't change the makeup of the Italian parliament, it underscores Salvini's rise from the head of a regional party in northern Italy to the country's most influential politician with an impact far beyond the country's borders.
Salvini has emerged as the informal leader of a group of nationalist and euroskeptic parties seeking to limit the European Union's influence on national policies, though it remains to be seen which of those parties will come together as bloc when the new European Parliament is formed.
Clutching a crucifix and casting himself as a defender of Europe's Judeo-Christian roots, Salvini noted that his colleagues in France and Britain also scored important victories. "Not only is the League the first party in Italy, but also Marine Le Pen is the first party in France, Nigel Farage is the first party in the UK," Salvini said. "It is the sign of a Europe that is changing."