Though his main opponent-Muharrem Ince of the secularist Republican People's Party (CHP)-has yet to officially concede, it appears Erdogan will now assume the significantly expanded powers he narrowly secured in a referendum a year ago.
There were another four candidates on the presidential ballot, all of whom fell below 10% of the vote.
Mr Erdogan, 64, returns to power after gaining a comfortable 52.6% of the vote - but his ruling Justice and Development Party suffered losses as it polled 42.5% in a parliamentary ballot.
Vladimir Potapenko, the deputy secretary-general of the Shanghai Cooperation Organization - one of the observer organizations for Turkey's Sunday elections - said in a news conference: "The elections is conducted in accordance with the legislation in force in Turkey, we confirm that all conditions necessary were provided for it". In view of the mobilization and enthusiasm of the opposition, expectations were high that the race could be forced into a second round, but Erdogan managed to pass the necessary 50 percent threshold.
He brought forward the elections from November 2019, but he reckoned without Ince, a former physics teacher and veteran CHP lawmaker, whose feisty performance at campaign rallies has galvanized Turkey's long-demoralized and divided opposition.
Although Erdogan dominated airtime on a pliant mainstream media, Ince finished his campaign with eye-catching mass rallies, including a mega meeting in Istanbul on Saturday attended by hundreds of thousands.
Erdoğan will assume vast new powers narrowly approved in a referendum a year ago, including the power to appoint senior judges and unelected vice presidents, and to pass decrees with the force of law. He also vowed to reverse what opposition parties see as Turkey's swing towards authoritarian rule under Erdogan. Had the HDP fallen short, its seats would have gone to the AKP.
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The amendments will transform the country from a parliamentary democracy into a presidential system - arguably the most significant political development since the Turkish republic was declared in 1923.
Under the new rules, the office of the prime minister is removed and executive powers are transferred to the president. The president will appoint senior judges, set the budget and can issue decrees as laws.
"A single person is becoming the head of the legislature, the executive, and the judiciary and this is a concern for a threat to the survival of the country", he told journalists.
The first greetings from an European Union country came from Hungarian Prime Minister Viktor Orban, according to Turkish presidential sources. "The rest of them talk about destroying what he has built". The country is split down the middle like an apple, with half of the country for Erdogan and the other against him.
Erdogan has compared Israel's actions in Hamas-controlled Gaza to Nazi policies. The president's prime challenger, Muharrem Ince, who had warned his supporters of possible fraud, had not conceded as of early Monday morning in Turkey. The imprisoned Demirtas obtained 8.4 percent, while Aksener - the only female candidate - only managed to score 7.3 percent. He has called the charges trumped-up and politically motivated. He has said his imprisonment was to silence him.
"The media environment, one of the candidates - Demirtas - being in jail, the new election legislation showed many irregularities happening ahead of the polls", she said.
Ince said he had garnered 15 million votes and would work to increase them to 30 million.
Reports of irregularities surfaced throughout the day.