Results for Tehran province, which is the country's most populous, showed a sweep by reformists and moderates of all its 30 parliamentary seats. Also, reformists won 15 of the province's 16 seats for the Assembly of Experts, a crucial body that would determine the country's next supreme leader.
Official results for the two national institutions are expected to be announced soon. But early indications at the reformers have scored well in these elections.
On Friday, voters had to select members of two crucial governing institutions: the Parliament and the Assembly of Experts. There are a total of 290 seats in parliament and 88 members for the Assembly of Experts.
How Iran's government works
The assembly chooses the Islamic Republic's supreme leader. Supreme Leader Ayatollah Ali Khamenei is 76 and has been rumored to be ill. If he were to die in the next eight years, the newly elected Assembly of Experts would select the next supreme leader.
Voter turnout for the elections was at nearly 60% of eligible voters -- which is about 33 million Iranians, according to Interior Minister Abdolreza Rahmani Fazli.
What it means for Rouhani
In many ways, the election has been seen as a referendum on Rouhani's policies, of which its centerpiece has been the nuclear agreement with the West. If Parliament does shape up to have more moderates and reformers, it would make it easier for Rouhani to push through his agenda.
"In this campaign Rouhani and his coalition have been saying that the nuclear deal was the first step to economic and political dignity, and that these elections were the next step," said Reza Marashi, research director at the National Iranian American Council, a nonpartisan, nonprofit organization promoting greater understanding between Americans and Iranians.
"If the election is favorable to Rouhani, it becomes his responsibility to fulfill campaign promises."
Many Iranian youths say life has improved under Rouhani. That demographic group's support is critical, as more than 60% of Iranians are under the age of 30, according to World Bank figures from 2013. Youth unemployment and underemployment have been significant issues for young people.
Meanwhile, conservatives express concerns about Western influence in the country. They accuse reformers of selling out to the West and have alleged foreign interference in the election.