Rahmati had been sacked two weeks ago after a huge argument with Shahr Khodro assistant Davoud Seyyed Abbasi in the club’s dressing room following a defeat to Sepahan.
He replaced Sohrab Bakhtiarizadeh in the Mashhad-based football team.
Shahr Khodro finished in sixth place in the Iran Professional League (IPL) last season.
The team will represent Iran in the 2020 AFC Champions League, which will be held in Doha, Qatar from September 14 to October 3.