Hassan Rohani has called his election as Iran's president a "victory of moderation over extremism."
Thousands of Iranians celebrated in the streets of Tehran after the outcome of the election was announced.
"This victory is a victory of wisdom, a victory of moderation, a victory of growth and awareness, and a victory of commitment over extremism and ill-temper," Rohani was quoted as saying.
"With their celebrations last night, the Iranian people showed they are hopeful about the future and, God willing, ethics and moderation will govern the country."
Rohani, a moderate cleric and former military commander and nuclear negotiator, was backed by Iran's pro-reform elements in the June 14 election.
He won nearly 50.7 percent of the more than 36 million votes cast, well ahead of five hard-line conservative rivals.
Rohani, in his first comments since his election win was confirmed on June 15, also called on world powers to treat Iran with respect and recognize its rights.
Supreme Leader Ayatollah Ali Khamenei, who has the final say in all strategic matters in Iran, congratulated Rohani.
In a statement on his official website, Khamenei urged "everyone to help the president-elect and his colleagues in the government, as he is the president of the whole nation."
Khamenei's quick endorsement of the results of the last presidential election in 2009, when conservative Mahmud Ahmadinejad won a second term despite allegations of fraud, helped spark widespread doubts that led to massive street demonstrations.
State television showed footage of the celebrations and on June 16 rebroadcast the speech Rohani made after his victory was announced.
Rohani will take office in August.
International responses to Rohani's election were cautiously encouraging.
The United States, which has had hostile relations with Iran for decades, said it "respected" the outcome and was ready for "direct" engagement to resolve allegations that Iran is trying to build a nuclear weapon.
European Union foreign policy chief Catherine Ashton said she was "fully committed" to working with Rohani’s government to resolve the nuclear dispute.
And United Nations Secretary-General Ban Ki-moon expressed hope that Iran would play a "constructive role" in regional and international affairs.
Israeli Prime Minister Benjamin Netanyahu noted on June 16 that it is the supreme leader, not the president, who decides on Iran's nuclear program.
Russian President Vladimir Putin urged Rohani to further strengthen ties with Moscow.
With reporting by Reuters, AFP, and BBC