Thousands of cars honked their horns throughout the capital, and many people were dressed in purple, Rowhani's campaign colour. Some even handed out purple balloons to the crowd.
"We said no to commander, we said no to mayor, (we chose) the courageous Rowhani," people chanted.
That was a reference to two defeated candidates, ex-Revolutionary Guards chief Mohsen Rezai and Tehran Mayor Mohammad Baqer Qalibaf, both hailing from the conservative camp.

More than 70 percent of Iran's 50.5 eligible voters went to the polls on Friday to elect a successor to Mahmoud Ahmadinejad, under whose presidency Iran has struggled to shore up an ailing economy targeted by harsh international sanctions.
Rowhani, 64, a moderate cleric who led talks with world powers over Iran's nuclear drive under president Mohammad Khatami, has vowed to re-engage the international community and fix the economy.
World reacts to the Rowhani's victory: Iran, France, UK
Reformist Hassan Rowhani, 64, has won Iran's presidential election with more than 50 per cent of the vote. UK, France, Syrian opposition and Iran's supreme leader Ayatollah Ali Khamenei already congratulated moderate cleric with his victory.
France on Saturday acknowledged the election of moderate cleric Hassan Rowhani as Iran's new president, saying it was "ready to work" with him on issues ranging from Tehran's nuclear drive to the Syria conflict.
"The expectations of the international community with regard to Iran are significant, especially about its nuclear programme and its involvement in Syria, " French Foreign Minister Laurent Fabius said in a statement.
"We are ready to work on them with the new president," he added as he praised the "Iranian people's resolute desire for democracy".
Britain on Saturday called on Hassan Rowhani to take Iran on a 'different course' following his victory in the country's presidential election.
"We call on him to use the opportunity to set Iran on a different course for the future: addressing international concerns about Iran's nuclear programme, taking forward a constructive relationship with the international community, and improving the political and human rights situation for the people of Iran," said a Foreign Office spokesman.
Also Iran's supreme leader Ayatollah Ali Khamenei on Saturday congratulated moderate cleric Hassan Rowhani on winning the presidential election, the website leader.ir reported.
"Congratulations to the people and to president-elect Hojatoleslam Hassan Rowhani," Khamenei's Internet site said."I urge everyone to help the president-elect and his colleagues in the government, as he is the president of the whole nation," he added.
The key opposition Syrian National Coalition umbrella grouping on Saturday urged newly elected Iranian President Hassan Rowhani to review his country's support for the Syrian regime.
"The Syrian National Coalition believes that it is its duty to call on the new president of Iran to rectify the mistakes made by the Iranian leadership," the group said, in reference to Tehran's staunch backing of Syrian President Bashar al-Assad.
Iran's president-elect Hassan Rowhani on Saturday in his statement hailed his election as a "victory of moderation over extremism," media reported.
"This victory is a victory for wisdom, moderation and maturity... over extremism," the mid-ranking moderate cleric who was also backed by reformists said.
Voice of Russia, AFP
Rowhani wins Iran presidential election - minister
Reformist Hassan Rowhani, 64, has won Iran's presidential election with more than 50 per cent of the vote, the Interior Ministry announced Saturday.
Moderate cleric Hassan Rohani has won Iran's presidential election, putting an end to eight years of conservative grip on the nation's executive, Interior Minister Mostafa Mohammad-Najjar announced on state television on Saturday.
Rouhani outclassed the other five candidates, especially the two close to the establishment: Hardliner Saeid Jalili and conservative Ali-Akbar Velayati.
Turnout in Friday's vote was 72 per cent. Observers had said that in case of a high turnout, Rouhani would also benefit from protest votes.
Conservative Mohammad Bagher Ghalibaf was in second place, while Jalili was in third.
Right after the official announcement, tens of thousands of Rouhani supporters gathered outside his election campaign office to celebrate his victory.
They shouted "Rouhani, take care of the country" and "Ahmadi, bye bye", referring to outgoing president Mahmoud Ahmadinejad.
Rouhani, 64, is a former chief nuclear negotiator and has vowed to seek a diplomatic solution in the deadlocked dispute over Iran's controversial nuclear programme by even entering into direct talks with arch-enemy United States.
The conflict with the West over Iran's nuclear programme was at the heart of the campaigns of all six candidates - all of who regard Ahmadinejad's nuclear policy as the source of the country's political and economic crises.
The moderate cleric has also promised to put an end to what he called the "eight-year dark era" of Ahmadinejad, by ensuring freedom of expression and liberty for the press.
The two candidates close to the establishment had high hopes because of the support of the clergy.
Rouhani will take office in August.
Iran: Rowhani close to victory in presidential elections
Reformist candidate Hassan Rouhani is taking the lead in the presidential elections in Iran. Experts are arguing about his chances of implementing the reforms.
Sergei Seregichev of the Institute of the Middle East is skeptical about the possibility of Tehran looking to the West or Washington turning towards Tehran.
“Until 1979, when Ayatollah Khomeini came to power, Iran played the role of ‘an aide to the sheriff’ while the role of the ‘sheriff’ belonged to the US. Now, countries that want the position of an ‘aide’, and these are Saudi Arabia and Qatar, are against Iran being reinstated in this role.
Modern Iran’s Chief Editor Igor Pankratenko is sure that Iran is in for change but these changes will be nothing else but a facelift.
“Anti-American rhetoric will take on a less aggressive tone. Iran is currently busy preparing a large package of proposals for Russia and the US on Afghanistan: what should be done following the withdrawal of US troops in 2014?”
Rowhani has 51% of vote in 65% of polling stations
Moderate cleric Hassan Rowhani has a clear lead in Iran's presidential election, garnering 51 percent of the vote at 65 percent of polling stations across the country, the interior ministry said on Saturday.
Rowhani, a former top nuclear negotiator, collected 11,754,013 votes of the 23,014,873 ballots to have been counted by 3:30 pm (1100 GMT), the ministry said.
Tehran Mayor Mohammad Baqer Qalibaf was in distant second place with 15.18 percent.
He was followed by former Revolutionary Guards commander Mohsen Rezai with 11.83 percent; Saeed Jalil, Iran's top nuclear negotiator, at 11.26 percent; Ali Akbar Velayati at 6.1 percent and Mohammad Gharazi at 1.2 percent.
 More than 50.5 million Iranians were eligible to vote to elect a successor to Mahmoud Ahmadinejad, who was constitutionally barred from standing again after serving two consecutive term