It is far too early to say whether Jesse Klaver’s GreenLeft will be a party of government for the first time in its history. But for the 30-year-old leader of a political party, the Netherlands’ youngest ever, it was not a bad election.

GreenLeft was the big winner in Wednesday’s poll, leaping from four MPs to 14 in the 150-seat parliament, topping the bill in Amsterdam and overtaking the stricken social democratic PvdA to become the largest party of the left nationally.

As traditional left and centre-left parties suffer across Europe in countries including Italy, France and Britain, the Dutch GreenLeft, formed 25 years ago by a merger of communists, pacifists, evangelicals and radicals, is growing fast.

A large part of its success is down to Klaver, a boyish figure in jeans, open-necked shirt and rolled-up sleeves who was first elected as an MP at the age of 24 and took over the leadership of GreenLeft in May 2015. Since then, under the “Jessiah”, as he is nicknamed, the party has gained 7,000 new members, nearly half of them under 30.

Something of a throwback to classic 1970s Dutch ideals of openness and radicalism, Klaver has a Moroccan father and a mother of Indonesian descent. The far-right populism of Geert Wilders, rather than Muslim immigration, is the real threat to Dutch culture and traditions, he has repeatedly said.

Properly leftwing parties in Europe had to fight the rise of the far right by standing up for their ideals, he said on Wednesday.

“What I would say to all my leftwing friends in Europe: don’t try to fake the populace,” he said. “Stand for your principles. Be straight. Be pro-refugee. Be pro-European. We’re gaining momentum in the polls. You can stop populism.”