The 28-year-old player has most recently played for the Saudi Arabian club Al-Jabalain.
Juma has joined Esteghlal on a six-month deal.
Masoud Juma has been a member of Kenya's national football team since 2017.
Kyrgyzstan striker Joel Kojo had also been linked with the Iranian team.
Esteghlal, headed by Pitso Mosimane, sits eighth in the Iran league’s 16-team table.