At midday on Monday, Stefanos Kasselakis, a shipping executive and former Goldman Sachs trader, walked through the corridors of the Greek parliament to be crowned head of Syriza, the country’s once radical leftwing party. No one could have seemed more out of keeping with a political force so steeped in the turbulence of Greece’s blood-soaked postwar history. But Kasselakis, a seemingly permanent smile on his lips, has defied all odds. After lighting up the skies of the country’s staid political scene with a campaign high on the vigour of social media, the 35-year-old Greek American has not only emerged as the winner of the two-round race to lead Syriza – gaining 56.69 % of the vote – but has proved he is far more than a shooting star. Barely six months ago, Kasselakis was a political unknown plucked from obscurity by Syriza’s outgoing leader, Aléxis Tsípras, to stand as an expatriate candidate on the party’s state ballot in national elections in May. Since leaving Greece as a teenager on a scholarship to a prestigious Massachusetts boarding school after winning a maths competition, he had not looked back. If screenwriters had been given the chance to write the script they might have stumbled. And not only because the erstwhile “Golden Boy” – a moniker bestowed on Kasselakis by columnists – comes from the US with a CV that no self-respecting leftist could endorse. In a Mediterranean country ill-prepared to elect a woman as prime minister – let alone an openly gay man – he has arrived in Greece with his husband, Tyler McBeth, a US nurse he met and fell in love with in Miami. McBeth, who like Kasselakis, starts his day working out in the gym, has appeared, smiling next to him ever since the leadership race began – the couple entered a civil union four years ago. “My mother,” the new Syriza leader said recently, “wants nothing more than for us to have children and be able to come help us.” On Sunday, Kasselakis went out of his way to ensure Greece’s socially conservative society knew exactly who his husband was, calling McBeth to join him in his victory speech outside party headquarters. Moreover, the rise of Kasselakis has appeared out of nowhere. The leftwing writer Dimitris Psarras, evoking the anxiety the Greek American’s sudden appearance has triggered among cadres in what had once been an alliance of Marxists, former communists, ecologists and social democrats, said: “It’s as if Netflix has come in, taken over the party and is now turning it into a serial. People have no idea what his politics are about, or whether he has a programme at all. Of course they’re in shock.” Addressing supporters as Syriza’s new president-elect, Kasselakis preferred the opaque language he has adopted since he announced his candidacy 27 days ago. “Today the light has won,” the political neophyte said. “And hope for the future.” It is a strategy that appears to have won over the majority of the nearly 134,000 voters who cast ballots in Sunday’s runoff. Although light on policy, Kasselakis, who volunteered on Joe Biden’s 2008 election campaign before working at a Washington DC thinktank, appears to have captivated Greeks precisely because he says little but ensures whatever he does say is positively positive. Of one thing the entrepreneur turned politician is certain: if Syriza is to govern again it has “to emulate” the US Democratic party and move to the centre left. His opponent, Efi Achtsioglou, a former employment minister who had signed up with Syriza in her youth, was the first woman to compete for the post and had long been considered the favourite. She sounded stilted and dull by comparison and in the end she gained 43.31 % of the vote. Although Greece’s main opposition party, Syriza’s leadership race may well have gone unnoticed had Kasselakis not injected an air of glamour into the contest when on 29 August he announced his candidacy via video on social media. With hindsight, the announcement could have been written by behavioural psychologists – the political newcomer has spoken publicly about having therapy to deal with his sexuality. Heavy on life story and truth, the statement starts: “My name is Stefano and I have something to tell you. I was born in Maroussi [an Athens suburb] in 1988, in a country with hereditary prime ministers; in a family with self-made parents. My mother a dentist, worked day and night to support my father while he started his company.” By the end of the video, Kasselakis has talked about the economic collapse of his family, how he ended up in the US “alone on a full scholarship”, attended the University of Pennsylvania, got a job at Goldman Sachs, entered the world of ocean shipping – making a small fortune in the process – and met “the breath of freedom” in his life, Tyler. His decision to join the Syriza leadership race – permitted for any paid-up member of the party – had, he said, been born of the desire “to build the Greek dream”. “I am aware that I have no party experience. My experience is in work and social life,” Kasselakis told listeners, insisting that with his better English, better business skills and better degrees, he could not only beat the Greek prime minister, Kyriakos Mitsotakis, but oust the centre-right from power. “For the Greek dream to become a reality, we must defeat those who benefit from a Greece that is a barren field and not Europe in practice,” he said. Whether he meant to or not, Kasselakis has done what no other person has managed to do: turn Greek politics into a pseudo-reality TV show in less than a month. But what he has also so aptly shown is that four weeks is a long time in politics, enough to erase the past and enough to “re-set” a party.