Twenty-seven conservative candidates were elected to parliament in Tehran, the last constituency to finish vote-counting, the national news agency IRNA said on Wednesday.
The latest results give the conservatives 156 seats in the 290-seat assembly.
In contrast, reformists have been decimated with just 39 seats. In addition, they can only contest 17 of the 58 seats that need a second round - pointing to a crushing rightwing majority when the new parliament convenes in May.
In another blow to the reformists, Parliamentary Speaker Mahdi Karrubi says he will withdraw from the second round of the elections after failing to secure his seat in the first, Aljazeera's correspondent reported.
Karrubi is an ally of the relatively reformist President Muhammad Khatami.
The election saw conservatives sweep aside their more liberal reformist opponents after the latter largely boycotted the poll last Friday.
The boycott came after Iran's Guardian Council, a conservative-dominated political watchdog, sparked a political crisis by barring around 2300 reformist candidates from standing. The ban included 80 sitting parliamentarians.
The results are a devastating blow to the reform camp. It swept to power in 2000 with a crushing majority in the Majlis but saw its efforts to democratise the country blocked by more powerful conservatives in the Guardian Council, judiciary or other rightwing strongholds.
They will also spell isolation for Khatami, who will be one of the few reformers left in public office before his second and final term ends in June 2005.