The leaders of Germany, Russia and many other countries gave their congrats after Erdogan secured reelection.
German Chancellor Olaf Scholz congratulated Erdogan on his election victory.
"Congratulations to President Erdoğan - together we want to advance our common agenda with a fresh impetus!" Scholz said on Twitter, hailing the two countries' close "partnership and alliance."
Russian President Vladimir Putin also congratulated Turkish leader Recep Tayyip Erdogan, saying his victory was "the logical result" of his dedicated work as head of the Turkish Republic. Putin also praised Erdogan for his "personal contribution to the strengthening of friendly Russian-Turkish relations."
Pakistan's Prime Minister Shehbaz Sharif described the long-reigning Turkish leader as a "pillar of strength for the oppressed Muslims" as well as an "ardent voice for their inalienable rights." Qatar and Iran also offered their congratulations.
The Turkish electoral authority declared Erdogan the winner of the election which will see him secure another five-year term.
"Based on provisional results, it has been determined that Recep Tayyip Erdogan has been elected president," Supreme Election Council chairman Ahmet Yener was quoted as saying by the Anadolu state news agency.
Opposition leader Kemal Kilicdaroglu pledged to continue "leading this struggle" against the Erdogan regime.
"My real sadness is about the difficulties awaiting the country," he said, without explicitly conceding defeat.
He also decried "the most unfair election in years" after projections showed him losing to the nationalist president.
The Turkish president spoke to supporters shortly after declaring victory, saying voters had given him the responsibility of governing for the next five years.
"The only winner today is Turkey," Recep Tayyip Erdogan said.
Erdogan addressed supporters on a bus in Istanbul, thanking people for coming out to vote. "God willing, we will be deserving of your trust," he added.
He also mocked his challenger for the loss, saying "bye bye bye, Kemal," as his supporters booed.
Turkey's Erdogan declared victory in the race, after both state and opposition affiliated media outlets put him in the lead with 97% of the vote counted.
The state Anadolu news agency showed Erdogan at 52.1%, and his challenger, Kemal Kilicdaroglu, at 47.9%.
The ANKA news agency, close to the opposition, put Erdogan's lead at 51.9%, with Kilicdaroglu garnering 48.1% of the vote.
Meanwhile, the country's official electoral authority has tallied 54.6% of the votes so far, the agency's chief Ahmet Yener said. Erdogan is leading with 54.47% of the votes, while Kiliçdaroglu has 45.53%, Yener added.