Foreign minister Abdullah Gul, of the ruling Justice and Development Party (AKP), looks likely to win the vote after an apparent boycott from the opposition party.
The Republican People's party (RPP) has declined to put up any serious competitors to Mr Gul's candidacy in a ploy which some commentators say aims to prompt earlier general elections.
"We may be members of different parties, but we are one people. Let's do our democratic duty under the same roof," the Associated Press news agency quoted prime minister Tayyip Erdogan as saying.
Although largely Islamic, Turkey has a long history of separating church and state. Its secular wing has pointed to the potential election of the Islamist Mr Gul as another step on the road to further integration of the two.
The AKP has sought to play down its mild Islamic policies. It prefers to emphasise its ongoing efforts to convince the EU that it is seeking internal change in line with its long-term goal of acceding to the European Union.
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