Iranian President Hassan Rouhani's allies have won all of the capital's 30 seats in parliament, state television reported on Sunday.
"The people showed their power once again and gave more credibility and strength to their elected government," Rouhani said and added he would work with everybody who won seat in the election to contribute future for the industrialised, oil-exporting country.
"Based on the votes that we have so far it looks like the Principlists will lose the majority in the next Majlis (parliament) shy of 50 percent. The reformists gained 30 percent and independent candidates did better than before, gaining 20 percent," said Foad Izadi, an assistant professor at the Faculty of World Studies in Tehran University.
"It is a sweeping victory for Tehran but for other cities it is not yet clear cut. It is beyond expectations," he said.
The head of Iran's conservative grand coalition of Principlists, Gholam Ali Haddad-Adel was set to lose his seat.
Many analysts say the election is a potential milestone for Iran, where almost 60 percent of its population is under 30 and willing to engage with the world after most of international sanctions lifted against the country.
Etemad, a reformist newspaper whose managing-editor Elias Hazrati got a seat in Tehran, has selected the first headline of "clean up in the parliament."
"The next parliament will be like no other parliament in the history of Iran as no political faction will have the absolute say," the newspaper said on its front-page.
Meanwhile, initial results show delegates aligned with moderate President Hassan Rouhani and his top ally and former president Akbar Hashemi Rafsanjani leading the polls for the Assembly of Experts, Iran's official IRNA news agency reported on Saturday.
During the vote, Rafsanjani's allies including Rouhani, performed well in the Assembly of Experts in Tehran. The assembly is responsible for choosing the Islamic Republic's highest authority, the supreme leader.
"The competition is over and the phase of unity and cooperation has arrived," state news agency IRNA quoted him as saying. "The time after elections is the time for hard work to build the country".
A political moderate, Rouhani is expecting an alliance with reformists which can eliminate the conservative dominance of parliament, facilitating his work to pass social and political reforms.
Early outcomes from Friday's polls said that none of the three main competing political groups will obtain a majority in the 290-seat parliament.
Alongside with 290 MPs, Iranians also voted for the assembly of experts - a clerical body empowered to choose or dismiss Iran’s supreme leader, who is currently Ayatollah Ali Khamenei.
Iran's state news agency IRNA reported that President Rouhani on Friday said he had received reports of a high turnout in twin elections for the parliament and the assembly of experts.
"Election is a symbol of the political independence of a country. By voting, people decide the future of their country ... reports shows a high turnout in the elections," Rouhani said.
The election will likely have an effect on whether the Islamic Republic continues repairing its ties with other countries after years of international isolation and sanctions. The vote is largely a referendum on moderate Rouhani following last summer's historic nuclear agreement, which curbed Iran's nuclear activities in exchange for lifting the sanctions.
Iran's supreme leader Ayatollah Khamenei called on "whoever likes Iran and its dignity and glory" to vote in elections after casting his vote on Friday.
"Iran has enemies," he said.
"They are eyeing us greedily. Turnout in the elections should be high to disappoint our enemies ... People should be observant and vote with open eyes and should vote wisely."
Before the elections he made similar remarks, saying that the West was plotting to influence the elections by pitting centrists close to President Rouhani against conservative hardliners.
Reformists seeking greater democratic changes and moderates supporting Rouhani frequently clash with the hardliners who oppose the nuclear deal and increasing ties with the West.
The conservative hardliners will likely have a strong influence on the makeup of both the parliament and the assembly of experts.
Some 53,000 polling stations throughout Iran have been receiving ballots for the 290-member parliament and the 88-member assembly of experts.
Nearly 55 million Iranians are eligible to vote in the elections.