TEHRAN, Iran—Partial results released Sunday indicate that Iranian reformists will win all 30 parliamentary seats contested in the capital, Tehran, handing hard-liners an embarrassing defeat in the first elections held since last year’s nuclear deal, which appears to be propelling moderates to their best nationwide electoral showing in more than a decade.
The deal is expected to bolster moderate allies of President Hassan Rouhani, who championed it in the face of hard-line opposition. However, none of Iran’s three main political camps—reformists, conservatives or hard-liners—is expected to win a majority in the 290-seat assembly.

A cleric waits for registration during the parliamentary and Experts Assembly elections at a polling station in Qom, 78 miles south of the capital Tehran, Iran, on Feb. 26, 2016. Iranians voted on Friday in parliamentary elections, the country's first since its landmark nuclear deal with world powers last summer. Majid Saeedi/Getty Images