Kemal Kilicdaroglu, head of the secular Republican People’s Party (CHP), spoke to thousands gathered for the event at an open-air site in the northwestern province of Canakkale.
“Eighty million have a thirst for justice,” Kilicdaroglu said, referring to Turkey’s population.
Kilicdaroglu earlier this summer walked 450 kilometres (280 miles) from Istanbul to Ankara to protest against the sentencing of one of his MPs, Enis Berberoglu, to 25 years in jail for leaking classified information to an opposition newspaper.
Under the simple slogan “justice”, the march culminated last month in a huge rally in Istanbul that attracted hundreds of thousands, the biggest event staged by Erdogan’s critics in years.
“It is my duty to seek justice. It is my duty to stand by the innocent and be against tyrants,” Kilicdaroglu told the crowds on Saturday.
More than 50,000 people have been arrested under Turkey’s state of emergency, imposed after a failed coup against Erdogan in July 2016, and almost three times that number have lost their jobs, including teachers, judges, soldiers and police officers.
Kilicdaroglu condemned the crackdown as a “civilian coup” — which took place for the first time in the history of the modern republic after the botched military putsch.
“Thousands of academics have been dismissed from universities,” the opposition leader said. “Prisons are full of journalists. MPs are in jail”.
Kilicdaroglu said Berberoglu’s sentencing “became the last straw.”
“We have a lot of citizens who are in prison just because they are in opposition,” he said. “To fight for rights is the duty of this country’s brave people.”
The congress will see several daily sessions on different rights violations in Turkey, the first time the CHP has held such an event.
Quoting the famous Turkish poet Nazim Hikmet, Kilicdaroglu said the theme of the congress would be: “To live like a tree, as free and independent, and also to be in the forests, all together, in peace.”
A photo depicting the CHP leader wearing a white undershirt while dining in a trailer during the justice march went viral on social media but drew Erdogan’s wrath because he said it was an insult to Turks.
Kilicdaroglu responded that Erdogan needed to address the “country’s problems” instead of “bothering with my vest from morning to evening”.
That speech from Kilicdaroglu was interrupted by applause from the crowds chanting “rights, law and justice!”.