Sanat Naft Abadan coach replaced his countryman Pedro Emanuel in the Saudi Arabian top-flight football team.
Sergio, who was appointed as Sanat Naft coach in June 2018, finished in eighth place in the Iranian league with the Abadan-based football team but was forced to leave the team due to financial issues.
Al-Taawoun came third in the Saudi Professional League this season behind Al-Nassr and Al-Hilal.
Al-Taawoun will participate in the 2020 AFC Champions League.