The incumbent faces a head-to-head with Kemal Kilicdaroglu after no overall winner was declared from the first round of voting.
Mr Erdogan won 49.51 per cent in the first round, with a slight lead over his rival and, should he be elected once more, he will continue a premiership that has lasted since 2003.
But while the Turkish leader has ruled with an increasingly tight grip, he is not the longest-serving leader in the world by any means and even longtime Russian president Vladimir Putin — who came into power in 1999 — is someway short of the list. Here are the top five longest premierships of current living heads of state.
Who are longest-serving world leaders?
5. Hun Sen — 1985
The name of the role has changed, but Mr Hun has effectively been Cambodia’s premier since 1985. He is now in his sixth term in the Asian country, which has one-party rule.
4. Ali Khamenei — 1981
Mr Khamenei has had various roles within Iranian politics but has effectively been at the summit since becoming president in 1981. Since 1989, he has occupied the position of supreme leader.
3. Teodoro Obiang — 1979
The second president of Equatorial Guinea assumed office in 1979. He is now 80 years old and reportedly wishes for his son Teodoro to succeed him.
2. Paul Biya — 1975
The president of Cameroon since November 6, 1982, Mr Biya is the longest consecutively serving current leader in the world as well as the oldest head of state, at 90 years old. Before taking the top job, Mr Biya had been prime minister from 1975 to 1982.
1. Hassanal Bolkiah — 1967
The Sultan of Brunei and prime minister of the south-east Asian country has ruled since October 5, 1967 — the longest of any head of state, including ceremonial monarchs, since the Queen died. And, at age 76, he could eventually beat her record.