Following the fall of the Sasanian Empire in 651, the Umayyad Caliphate, which emerged as the ruling power, adopted many Persian customs, especially in administration and court culture. Provincial governors during this period were often Persianized Arameans or ethnic Persians. Persian remained the official language of the caliphate's business until the end of the 7th century, when Arabic gradually replaced it, evidenced by the Arabic script replacing Pahlavi on coinage starting in 692 in Damascus.^[32]

The Umayyad regime enforced Arabic as the primary language in its territories, often forcefully. Al-Hajjaj ibn Yusuf, disapproving of the widespread use of Persian, ordered the replacement of local languages with Arabic, sometimes by force.^[33] This policy included the destruction of non-Arabic cultural and historical records, as described by al-Biruni regarding the conquest of Khwarazmia.

The Umayyads also established the "dhimmah" system, taxing non-Muslims ("dhimmis") more heavily, partly to benefit the Arab Muslim community financially and discourage conversions to Islam, as conversions could decrease tax revenues. During this time, non-Arab Muslims, like the Persians, were considered mawali ("clients") and faced second-class treatment. The Umayyad policies towards non-Arab Muslims and Shias created unrest among these groups.

Not all of Iran was under Arab control during this period. Regions like Daylam, Tabaristan, and the Mount Damavand area remained independent. The Dabuyids, especially Farrukhan the Great (r. 712–728), successfully resisted Arab advances in Tabaristan.

The Umayyad Caliphate's decline began with the death of Caliph Hisham ibn Abd al-Malik in 743, leading to civil war. Abu Muslim, sent by the Abbasid Caliphate to Khorasan, played a key role in the Abbasid revolt. He conquered Merv and effectively controlled Khorasan. Concurrently, Dabuyid ruler Khurshid declared independence but soon acknowledged Abbasid authority. The Umayyads were ultimately defeated by the Abbasids at the Battle of the Zab in 750, leading to the storming of Damascus and the end of the Umayyad Caliphate.