Why is Persian written with a version of the Arabic script?

The use of the Arabic script for the Persian language is a result of the Islamic conquest of Iran in the 7th century CE, which brought both the religion of Islam and the Arabic language to the region.1

Prior to this, Persian was recorded using various forms of the Aramaic script, such as the Pahlavi alphabet. However, these earlier scripts were often considered inadequate or ambiguous for recording the language precisely. As the Arabic script spread across the Eastern Hemisphere with the expansion of Islam, it was adopted and adapted to fit the phonology of Persian.23

To accommodate specific Persian sounds not present in Arabic, four letters were added to the script using diacritical marks. Over time, the script evolved into distinct styles, such as the Nastaʿlīq script, which became the primary method for writing Persian. This adaptation allowed the language to maintain its literary tradition while integrating into the broader cultural and religious framework of the Islamic world.231