More than 56 million voters began gathering outside polling centers 8 a.m. local time to cast their ballots.
Five candidates are running against him in the presidential race.
Former physics teacher Muharrem İnce is backed by the main opposition Republican People’s Party (CHP) and has wooed crowds with an engaging election campaign. His rallies in Turkey’s three main cities of Istanbul, Ankara and İzmir drew massive numbers.
Also challenging Erdoğan is 61-year-old former interior minister Meral Akşener. The only woman candidate broke away from Turkey’s main nationalist party over its support for Erdoğan and formed the center-right and nationalist Good Party (İYİ Party).
Selahattin Demirtaş, the candidate of the Kurdish issue-focused Peoples’ Democratic Party (HDP) was forced to run his campaign from prison, where he is being held in pre-trial detention on terrorism-related charges.
Felicity Party (SP) leader Temel Karamollaoğlu and Patriotic Party (VP) leader Doğu Perinçek are also running for the post after collecting 100,000 signatures from citizens to be nominated.
Turkey will also be electing 600 lawmakers to parliament - 50 more than in the previous assembly.
The HDP was left out of the alliance and needs to pass a 10 percent threshold to win seats in parliament. If the party passes the threshold, it could cost the “People Alliance” dozens of seats.