As a populist surge shook the EU to its foundations, Italy's young centre-left prime minister bucked the trend. Now, he says, he can set the agenda in Brussels

Matteo Renzi breezes through the gilded wooden doors in jeans, D'Acquasparta trainers and rolled-up shirt sleeves. "Today, I am tie-less," he announces, disingenuously apologetic, perhaps, for a man with a much-photographed leather jacket.

Dress-down Friday? "Absolutely," he replies in English and grins. In a salon with a long history and a one-note colour scheme – gold – the contrast in style between Palazzo Chigi and its occupant has probably never been more striking. Yet, sitting back on a delicate, gleaming-legged sofa, Italy's cocksure young prime minister could not seem more at home.

Few mainstream politicians will look back at last week's European elections with anything other than gloom. From London to Paris to Copenhagen, leaders on the centre-left and centre-right were dealt a bloody nose by voters who chose instead to throw in their lot with populists, Eurosceptics, and the far right. In Rome, however, a different story played out. In its first election with Renzi as leader, his centre-left Democratic party (PD) beat all expectations to come not only first, but first by an astonishing margin of almost 20 points.

With almost 41% of the vote, the PD had performed better than any Italian party since 1958. It had left its chief rival, the anti-establishment Five Star Movement (M5S), in the dust. It had won more votes than any other party in the EU and had become the second-largest force in the European parliament.

After years of lectures, humiliations and knuckle-rappings, Italy was back on the European stage, credibility – so the government said – restored. And Renzi, a 39-year-old who not even six months ago was the ambitious mayor of a provincial city, finds himself not only prime minister but one of the most important advocates for Europe in a fearful and crisis-struck union.

Renzi says the main task is to get Europe out of crisis. Photograph: Rex Features

On arrival in Brussels last week, Renzi was greeted by Angela Merkel as "the matador". He has been hailed by some commentators as the sole leader who, amid François Hollande's seemingly inexorable demise, has enough clout to hold the centre-left line with the German chancellor. For Renzi it is undoubtedly a huge personal triumph, a victory that earns him the popular mandate he had been lacking until now, having taken power earlier this year from a party rival.

But, as with any smart politician, he is unwilling to be seen to bask in glory.

"I do not think the meaning of the elections was the birth of Matteo Renzi, leader," he says, in an interview with the Observer and four other leading European papers. "The meaning of the elections is: Italy can play a role; Italy is not the last wheel of the wagon; Italy is not the bottom of the class. Italy is a country which, if it changes itself, can also be one of the leaders in Europe and, in this sense, the point is not to seek out privileged axes with some countries rather than others, but to try to get Europe out of the crisis situation which we are in."

In something of a double whammy, the PD's historic win comes not long before Italy takes over the EU's rotating presidency, a period during which an emboldened Renzi hopes to get to work on the change in Brussels he believes is needed to keep the European dream alive.

"I say that if we want to save Europe, we must change Europe. Even in our country, those who voted PD were also asking for Europe to be changed, not kept as it is," he says. What he does not add is that his party's share of the vote was exceeded by the number of Italians who cast their vote for parties that, to varying degrees, ran Eurosceptic campaigns: Beppe Grillo's M5S, on 21.2%; Silvio Berlusconi's Forza Italia, 16.8%; and the Northern League, 6.2%.

Firmly on the to-do list in Brussels, he says, is the need to "change the paradigm of economic politics"; a move, in essence, away from undiluted austerity. He has "an excellent relationship" with Merkel and insists that Germany is "not an enemy" but a model of reform in many ways. But "this does not mean there isn't the possibility of having different ideas on many issues; among other things we belong to two different political families [in Europe]", he cautions.

"It is very clear today that it is in Germany's interests for Italy to do well. And Italy has all the conditions needed for doing well, provided that Europe's basic setting is not focused solely on austerity but also on growth; on growth, employment and reforms. This is our aim. And without a big investment on jobs and on growth, any measure linked to austerity is destined to fail."

For the moment, he says, what Europe does is more important to him than who gets which job: a neat way – accompanied with a flourish of Latin, "Nomina sunt consequentia rerum" – of avoiding getting too involved in the battle over the top posts coming up soon in Brussels, primarily that of commission president. He does not explicitly say whether or not he backs Jean-Claude Juncker, the divisive pick of the Christian Democrats who is supported by Merkel but rejected by David Cameron. Still, he notes that "it's hard to imagine that a person could be chosen [as commission president] without an overall agreement".

Renzi knows that, despite the unexpectedly big boon last week's poll has given him, Italy will hold no great sway in Europe if it cannot put its own house in order first. He insists that his reform agenda – aimed at making the eurozone's third-largest economy more politically stable and efficient, less mired in bureaucracy and vulnerable to corruption, more fertile for the growth that has proved elusive for years – is "changing Italy deeply". (His critics say it has barely begun, and, where it has, for instance in modest labour reform, it threatens to change the country for the worse, not the better.)

The European poll gives Renzi the blessing at the ballot box that he did not technically need but whose absence was felt keenly by some voters. When he ousted Enrico Letta from power in February in a party rebellion, the then mayor of Florence and recently elected head of the PD faced a barrage of criticism from those who found it jarring that a politician who had always styled himself as the nemesis of the political old guard took power in what they saw as a straightforward coup.

Even now, the suggestion rankles. "There was not a plot … as some wanted to suggest. The government in question went through a process of burnout," says Renzi. "To deny it now is very convenient but also very unfair and I have suffered greatly on a personal level from this version of events."

What of his now infamous television interview, recorded little more than a month before he was sworn in, in which he declared: "Enrico, keep calm; no one wants to take your job"?

The words returned to haunt Renzi for weeks afterwards, in the fitting form, for this most Twitter-friendly of premiers, of contemptuous hashtags and YouTube satire.

"I said that sentence because I was convinced of it," he says. "At that time I was pushing the Letta government to get moving again. It was like a car whose battery had run down."

Renzi is Italy's fourth prime minister in less than three years. "I don't know if it's a good or a bad thing, but I think that you won't see any more for a few years," he says, smiling.

If he leads his current coalition government through a full term, he will be in Palazzo Chigi until at least 2018. But in Italy, that is a big "if". Only one man has led a postwar government to a full five-year term: Berlusconi.

Damaged by splits to the centre-right and his conviction for tax fraud, Berlusconi recorded his worst-ever result in last week's poll. The M5S's result was described by Grillo as "beyond a defeat". But, especially as he sees the rising stars of Nigel Farage in the UK and Marine le Pen in France, Renzi knows that, huge majority or no, he cannot afford to underestimate either.

"Basically, it comes down to us: Are we carrying out reforms? Are we putting up a fight against the cost of politics? Are we investing in simplification? Are we in the piazzas? If so, we win," he says.

"If [mainstream] politics becomes convinced that it has survived the danger and goes back to shut itself away again, the M5S will come back with great strength. If we had not done an electoral campaign in the midst of the people, in the piazzas – hard-nosed and open-faced in a very strong way – we would have been carried away, as happened in other countries."

The rise of Renzi



December 2012: Renzi, mayor of Florence, fails in his attempt to become PD leader. Loses primary to party stalwart Pier Luigi Bersani

February 2013: Bersani's PD fails to make good on pre-election lead and enters weeks of negotiations to try to form a government following general elections

March/April: Bersani says he cannot form a government. Renzi's name is briefly mentioned as a potential candidate for prime minister but is rapidly forgotten as Letta is asked instead

December: Renzi runs again for PD leadership and wins by a landslide. Vows to work alongside government for reform

January 2014: Amid frequent criticisms of the Letta government, he strikes a controversial cross-party reform pact with Berlusconi

February: Renzi moves against Letta and receives backing of PD leadership. Letta quits. Renzi is sworn in and becomes Italy's youngest-ever prime minister

May: Under its new leader, the PD wins big at the European elections

•Fabio Martini (La Stampa), Andrea Bachstein (Süddeutsche Zeitung), Philippe Ridet (Le Monde) and Pablo Ordaz (El País) contributed to this report