Opposition to Turkey’s authoritarian president, Recep Tayyip Erdoğan, has been re-energised by the success of a month-long, cross-country anti-government “justice march” and last weekend’s unprecedented mass rally in Istanbul attended by more than a million Turks.

The show of strength momentarily shocked the government into nonplussed silence. This week is supposed to be dominated by a series of official events marking the first anniversary of the 15 July attempted coup – the planned culmination of which is Erdoğan’s address to parliament in the early hours of Sunday morning, exactly a year since the attempt was launched.

Erdoğan will stress the perils the nation has faced and his own heroic steadfastness, by way of justifying his subsequent harsh crackdown. But the anniversary is being dominated instead by excited talk of a resurgent Turkish democracy, led by Kemal Kilicdaroglu of the centrist main opposition party, the Republican People’s party (CHP). He has vowed to fight Erdoğan’s “one-man regime” and overturn what he calls the “second coup” – the Erdoğan power grab that has followed the failed putsch.

Turkey was on the brink of “a new beginning” after one of the darkest periods in its recent history, Kilicdaroglu told an estimated crowd of 1.5 million people in Istanbul on Sunday. “It’s a new climate, a new history, a new birth,” he said.

A shy, unassuming man, Kilicdaroglu has often been dismissed as a political lightweight. But his show of defiance has transformed his image and that of the CHP, and mitigated the sense of hopelessness many Turks feel about the repressive political climate.

“Turkey is no longer the country of 25 days ago,” said Murat Yetkin, a columnist for the Hurriyet newspaper . “There are signs that the pacifistic but huge action of the justice march … has started to change the ruling Justice and Development party’s (AKP) stance. It may also have changed … the wider political culture in Turkey.”

About 190,000 people have been detained, fired or suspended from their jobs since the coup attempt, which Erdoğan is accused of exploiting to neutralise opponents. They include judges, army and police officers, lawyers, academics, politicians and journalists. Kilicdaroglu has been widely abused and threatened by AKP officials and supporters, and condemned as subversive and a traitor.

Facebook Twitter Pinterest Kemal Kilicdaroglu is said to have reinjected hope in millions of Turks. Photograph: Yasin Akgul/AFP/Getty Images

Erdoğan went even further, at one point condemning the justice marchers as terrorists. But as people from different, non-political backgrounds rallied to Kilicdaroglu’s banner, Erdoğan was forced to back off. This was partly because polling showed scant public sympathy for his stance. Even AKP supporters were unhappy, particularly over the politicisation of the judiciary, Yetkin said. The march was supported by the main pro-Kurdish opposition party – whose co-leader, Selahattin Demirtas, is in jail on terrorism charges – as well as trade unionists and other civil society groups, and ordinary citizens.

“No one expects an overnight miracle [but] Kilicdaroglu has reinjected hope in millions of Turks who are deeply worried about the rapid deterioration of their democratic and secular system,” wrote Semih Idiz, a commentator. “The government was caught completely off guard by this act of protest [that] garnered a lot of public sympathy on the way.”

Kilicdaroglu is now trying to build on the momentum by pushing a list of 10 demands. They include restoring parliament’s authority, lifting the state of emergency, re-establishing judicial independence and releasing detainees. The effect would be to roll back sweeping executive powers granted to Erdoğan after he narrowly won last April’s constitutional referendum.

Kilicdaroglu promised further street protests and warned on Tuesday against AKP attempts to “abuse” the commemorations. He is also organising what he calls “the world’s biggest petition” on behalf of the detainees, some of whom are taking legal action in the European court of human rights.

An AKP spokesman, Mahir Unal, said the CHP leader was playing a dangerous game and accused him of encouraging anarchy. “If you are calling on people to hit the streets, this is fascism,” Unal said this week. But Erdoğan has remained unusually quiet.

Increasingly vocal domestic resistance is putting growing international pressure on Erdoğan to ease his iron grip on Turkish society. Relations with the EU commission and European parliament are already strained. The US ambassador to Turkey recently urged the government not to abuse its counter-terrorism powers. And the Netherlands and Austria have followed Germany in refusing to allow Turkish ministers to address expatriate Turks on the coup anniversary.