With nearly all ballots counted, main opposition party candidate Ekrem Imamoglu had a lead of 775,000 votes, a huge increase on the margin of 13,000 he achieved in the earlier election.
That victory in March was annulled after the AKP alleged irregularities.The result ends 25 years of AKP rule in Istanbul.The AKP’s candidate, former Prime Minister Binali Yildirim, conceded to his opponent.
On Twitter, President Recep Tayyip Erdogan wrote: “I congratulate Ekrem Imamoglu who has won the election based on preliminary results.”
Mr Erdogan had previously said that “whoever wins Istanbul, wins Turkey”. He has ruled the country since 2003 both as prime minister and now president, becoming the most powerful leader since Mustafa Kemal Atatürk, the founder of the modern Turkish republic.
In his victory speech, Mr Imamoglu, of the Republican People’s Party (CHP), said the result marked a “new beginning” for both the city and the country. He said his supporters had “fixed democracy”.
“We are opening up a new page in Istanbul,” he said. “On this new page, there will be justice, equality, love.”
He added that he was willing to work with Mr Erdogan, saying: “Mr President, I am ready to work in harmony with you.”
With 99% of votes counted, Mr Imamoglu had 54% of the vote and Mr Yildirim 45%.