Sunday's victory will extend Erdogan's more than 10-year rule over the country for another five years.
"The provisional results show that Erdogan has the majority of the valid votes," High Election Board chairman Sadi Guven told a news conference in the capital Ankara.
"We have received more than 99 percent [of the votes]. Tomorrow we will announce the provisional results," Guven said on Sunday.
Erdogan declared victory by addressing his supporters from his party's headquarters in Ankara.
"Today national will and democracy have prevailed again… Today, greater Turkey has prevailed again... With the president being elected by popular vote, obstacles between Cankaya [the presidential palace] and the public have been lifted," he said, striking a conciliatory tone after a tense campaign period.
"Our political views, lifestyles, beliefs and ethnicities can be different, but we are all offspring of this country. We are all owners of this state... I will embrace all 70 million [Turks] as president."
The vote has been seen as a milestone in Turkish politics as Turks are electing their president by a popular vote for the first time in the country's history, bringing new legitimacy to the office.
In a brief statement to reporters in Istanbul, the main opposition candidate Ekmeleddin Ihsanoglu said, "I congratulate Mr Prime Minister and wish him success."
At midnight (9pm GMT) on Sunday, the prime minster had received 52 percent of the votes, Ihsanoglu won 38 percent and the third candidate, Selahattin Demirtas, took in 10 percent, after 99 percent of the votes had been counted, the semi-official Anatolia news agency said.
NTJ/MB