To be in Poland on Sunday night was to experience a rare moment of political joy. Young voters queued until the early hours to see off the xenophobic, nationalist populists who have been dragging their country backwards; to prove that even an unfair election can be won against the odds; and to turn Poland towards a modern European future. If you were already in the queue at 9pm, when polls closed, you were allowed to wait to vote. Some of the queues were very long, so neighbours brought hot drinks to sustain people in the cold. Interviewed at about 1am on Monday, one young man in Wrocław said he had to hang in there because this was the most important election since 1989. I walked to a Warsaw polling station on election day with the same old friends whom I had accompanied to that historic vote on 4 June 1989. With delight, they each chose one name from the long list of parliamentary candidates. With equal delight, they refused even to take the ballot paper for the simultaneous referendum, which – with its ludicrously biased questions about things like an alleged “forced relocation mechanism” for illegal immigrants, supposedly “imposed by the European bureaucracy” – was effectively election propaganda for the ruling Law and Justice party (PiS). But my friends and I were full of nervous anticipation. Anna told me that whereas in 1989 her dominant emotion had been hope, now it was fear. Her daughter, who was just seven in 1989, worried what more the ruling party could do to poison young minds and ruin her own seven-year-old daughter’s education should they win another term. But then, starting with the first exit polls at 9pm, our foreboding turned to relief and then joy. Despite being only semi-free, that 1989 election opened the door to democracy in Poland. And despite being unfair in multiple ways, not least in the crude, mendacious propaganda pumped out by all state-controlled media, this one should reverse Poland’s slide towards the kind of electoral authoritarianism practised by Viktor Orbán in Hungary. The record turnout, at nearly 74% on the current count, was 10% higher than in 1989. Reversing a continent-wide trend, first estimates suggest that voters under 29 turned out in larger numbers than those over 60. It seems young Poles finally understood that their future was at stake. Whatever happens next, this was a great democratic moment. The people spoke and said they wanted a different government. Unless current projections are badly wrong, the democratic opposition parties will have a clear parliamentary majority over PiS and its potential partner, the wild Konfederacja party, which had threatened to pick up a significant youth vote. Why did the opposition win? We will need more time to understand this fully, and there always remains a fog of glorious mystery around how and why millions of individual people ultimately decide to vote one way rather than another. Nonetheless, we can see that many voters simply got fed up with the corrupt, petty, backward-looking, obscurantist rule of the party led by the 74-year-old Jarosław Kaczyński, who is a kind of one-man walking anthology of resentment. Some were alarmed by opposition warnings that the anti-Brussels course of PiS might lead to Polexit. As well as the increased youth vote, for the first time ever more women than men voted in this election. Part of their motivation seems to have been the sight of a reactionary, patriarchal party imposing one of the strictest anti-abortion laws in Europe. More than 600,000 Poles abroad registered to vote, although their impact on the actual result will be (unfairly) marginal. Huge credit must go to Donald Tusk, the leader of the largest opposition list, the Civic Coalition, which has at its core the Civic Platform party that he co-founded in the early 2000s. I must confess I was sceptical about the return to the frontline of Polish politics of the 66-year-old former president of the European Council. It felt a bit like Tony Blair resuming the leadership of the British Labour party – and, as with Blair, there are a lot of people who can’t stand Tusk. But he fought his way through a barrage of poisonous abuse, ludicrously accusing him of being the German candidate, and this victory is in significant measure his. I came to Warsaw directly from Istanbul, where my liberal democratic friends are in deep depression after a united opposition failed to defeat president Recep Tayyip Erdoğan in an election earlier this year. In spring 2022, I watched a united opposition in Hungary go down badly against Orbán. In Poland, my friends and I were also urging the opposition to unite, which it failed to do. Yet it may turn out that the fact there were three different opposition lists to choose from – Tusk’s Civic Coalition, the Third Way (combining two parties broadly acceptable to liberal Roman Catholic voters) and the New Left – actually ended up maximising the opposition vote. It’s still early days. Resentment-filled Kaczyński may yet have a few dirty tricks up his sleeve. President Andrzej Duda will almost certainly give him the first chance of forming a government, so it could take months before power finally changes hands. Such a diverse opposition coalition may be fractious in government (think Germany). Then there will be the huge challenge of reversing PiS’s creeping state capture. I just learned a new Polish word: depisyzacja, that is, dePiSisation, by analogy with decommunisation. But taking the PiS out of the Polish state will be a tough task. It means restoring the independence of the courts, turning state media into proper public service media, undoing deep political penetration of the civil service and state-owned enterprises, redrawing constituency boundaries so they reflect population changes, and more. All this while Duda still has extensive veto powers. Restored EU funding will help, but no one knows the true condition of Poland’s public finances and there’s a war grinding on next door in Ukraine. PiS remains the party that won the single largest share of the vote. In big cities, nearly half the votes went to opposition parties and less than a quarter to PiS, but in the countryside it was the other way round. Civic Platform must show it has learned from its mistakes in the 2000s and respect the concerns of a poorer, more conservative, Roman Catholic, rural and small-town Poland. And the opposition needs to avoid the temptation simply to take revenge – a temptation wonderfully depicted in Andrzej Wajda’s film of the classic 19th-century Polish comedy Zemsta (Revenge), which sees two Poles who share a castle furiously trying to do each other down. But sufficient unto the day are the evils thereof. I noticed this morning that the presenters on the independent, opposition-supporting TV channel TVN can hardly stop smiling – and, frankly, nor can I. Poland’s populist nightmare is almost over and all of Europe will benefit as a result. Timothy Garton Ash is a Guardian columnist