The 31 March vote in Turkey’s commercial capital was annulled after the AK Party of President Recep Tayyip Erdogan, which has governed Istanbul for the past two decades, alleged fraud.
But critics say Erdogan was simply unhappy when the opposition candidate, little-known former district mayor Ekrem Imamoglu, stole a slim victory of just 13,000 votes.
The number of media waiting for opposition mayoral candidate @ekrem_imamoglu to cast his vote in the repeat #Istanbul elections. The room is full to the absolute brim. #İstanbulSecimleri pic.twitter.com/6tfL7X6haZSeref Isler (@seref_i) 23 juin 2019
After being stripped of his win, Imamoglu, of the secular Republican People's Party (CHP), is now a household name – and the Istanbul rerun has become a test of Turkish democracy.
While the March elections showed Erdogan's AKP remains the most popular party, the result also came as a blow, with the party losing control of the capital, Ankara, as well as Izmir, Turkey’s third largest city.
Polls on Sunday opened at 8am local time and are to continue through to 5pm (1400 GMT) in more than 31,000 ballot boxes across Istanbul’s 39 districts.