A crowd of over 100,000 people thronged the Rome piazza, ferried in from around the country by eight special trains and 400 coaches for the “Italian Pride” demonstration.
“We were right to abandon this government,” the head of the far-right League party thundered, after speeches by a string of far-right leaders as well as billionaire former prime minister Silvio Berlusconi.
The anti-migrant Salvini pulled support from the previous populist government over the summer in a bid to spark elections he was convinced he could win to govern the eurozone's third-largest economy alone.
That plan failed when his former coalition partner, the anti-establishment Five Star Movement, sealed a deal with the centre-left Democratic Party to form a new, pro-European government.
After suffering a blip, the League's popularity has risen slightly again in the opposition role Salvini is more used to.
“I want to live in a free country, where you can govern without waiting for a phone call from (German Chancellor Angela) Merkel or (French President Emmanuel) Macron,” the eurosceptic Salvini said.
Recent opinion polls put the anti-immigration party at between 30 to 33 percent of voter intentions, well ahead of the Five Star (M5S) and Democratic Party (PD), which have dropped slightly to between 18 and 20 percent each.
With the current left-leaning government seeking to change the electoral law to prevent Salvini triumphing alone at the next elections, the 46-year-old hopes to unite parties on the right and centre-right under his leadership.
That, however, will not be an easy task.
Forza Italia head Berlusconi, 83, whose party has been in a lengthy slump, appears open to just such an alliance, along with the smaller, far-right Brothers of Italy.
“We're here in this piazza because we have a big responsibility, to answer our people's call for unity,” Berlusconi said, attacking the current government as “the most left-wing” since the war.
Brothers of Italy leader Giorgia Meloni, who had earlier complained that only League banners were visible on the podium, vowed to fight what she called “the Islamisation of Europe”.
“Let's fight this battle together beyond the confines of individual parties, without selfishness and we will be unstoppable,” Meloni said.
Some Forza Italia members had voiced unhappiness about the presence of neo-fascist party CasaPound at the rally.
Salvini in August had refuted the idea of a tie-up with Forza Italia, saying the League “needs nothing and no-one”, but on Saturday he reversed course and appealed for unity.
“I would like that, since the team always wins and never alone, the embrace of this square should also go to Giorgia Meloni and Silvio Berlusconi, because together we win,” Salvini said after his speech.
City needs love
Political analysts say Salvini has set his sights on taking Rome and hopes the right-wing alliance could carry him to victory in key upcoming regional elections, potentially setting him up for a win on a national level.
“Now there's only one thing to do, go to the polls because we other Italians, we citizens have the right to vote,” League supporter Marco Diurno, 58, told AFP. “Let's hope that Salvini returns us to an Italy of dignity.”
The next general election is not due until 2023, but the current governing coalition of former foes is shaky and might not last.
Salvini has waged war on Rome's mayor, M5S member Virginia Raggi, calling for her resignation, and has launched a petition demanding she step down now, two years before her term is due to end.
'Hands off Rome'
Raggi, 41, has come under intense fire for the city's ongoing garbage crisis and beleaguered transport services, which have existed for decades. She has blamed the problems on organised crime and corruption in previous administrations.
“Today we still hear many politicians who have miraculous recipes for Rome and for Italy, politicians who have governed in the previous decades,” Raggi said after the right-wing rally.
“If you have all these recipes why didn't you apply them when you were governing?” she asked on Facebook.