Najafi appeared in court on Saturday morning for the first time to stand trial for murdering his wife, Mitra Ostad, with a handgun.
Ostad was found dead at her home in Tehran on May 28 with gunshots in her chest.
A few hours later, the former mayor surrendered himself to the Criminal Police and confessed to killing his wife.
Najafi has cited family problems for the murder.
Najafi, 67, was elected mayor of Tehran in August 2017, but resigned in April 2018 for what he called poor health conditions.
Affiliated with the ‘reformist’ political parties, Najafi served as the minister of education and the minister of higher education in various administrations.
He also took the helm at Iran's Cultural Heritage, Handicrafts and Tourism Organization (ICHHTO) during President Hassan Rouhani’s first term, but resigned after six months.