While exit polls put the party on 27-31 per cent, by the time votes had been counted on Monday morning, the League had reached a staggering 34.3 per cent.
Gaining the second highest number of votes was its opposition, the centre-left Democratic Party (PD), who garnered 22.7 per cent.
The League’s ruling coalition partner, the anti-establishment Five Star Movement (M5S), took just 17.1 per cent of the vote.
Forza Italia (FI), the centre-right party founded by former prime minister Silvio Berlusconi, won 8.8 per cent – less than in the last EU elections but enough to get its leader a seat – while the far-right Brothers of Italy (FdI) took 6.5 per cent.
No other parties secured the 4 per cent minimum required to get one of Italy’s 73 seats in the European Parliament.
A triumphant Salvini kissed a rosary cross as he thanked “those up there” for his party’s resounding victory.
“One word: thank you Italy,” Salvini tweeted 90 minutes after polls closed on Sunday night, posting a photo of himself with a banner which read “1st party in Italy thank you”.
But Salvini warned the festivities would only last “a few minutes” as “now is the time for responsibility”.
“Millions of Italians have entrusted us with a historic mission,” he added.
“That is to bring to the centre of the European debate the right to have stable jobs, the right to healthcare, to have babies.”
The League’s success will affect the balance of power in its already fragile national coalition with the M5S, which has lost supporters since garnering the majority of votes in the national elections last year.
With the rise of the League, political commentators are speculating that Salvini could go back on the coalition’s agreement and force an early election.
“At a national level nothing’s changing,” Salvini declared at a press conference on Sunday night.
“We’re the first party in Italy, now Europe’s going to change.”
The League will take around 28 or 29 MEPs to Brussels, putting it on a par with the UK’s Brexit party and the Union parties in Germany.
The PD will have up to 19 seats, M5S 16, FI eight and FdI six.
Voter turnout in Italy was 56.1 per cent, down from 58.7 per cent in the last European election in 2014, making it one of the few countries where voter engagement decreased.