Islam did not “take over” Iran in a single year; it was a gradual process that began with the Arab-Muslim conquest in the 7th century and unfolded over several centuries.

Quick Scoop: Key Dates

  • Military conquest starts: Around 633–637 CE, during the rule of the second caliph, Umar, Muslim armies invaded Sasanian Persia.
  • Fall of the Sasanian Empire: The last Sasanian king, Yazdegerd III, was killed around 651 CE, marking the effective end of the pre-Islamic imperial state.
  • Conquest of major eastern regions: By about 674 CE, Muslim forces had taken Greater Khorasan (including parts of today’s Iran, Afghanistan, and Central Asia).
  • Islam becomes majority religion: Research on conversion patterns suggests that most Iranians were still not Muslim at first; Islam only became the majority faith by roughly the 10th century (around 950 CE), after generations of gradual conversion.
  • Shift from Sunni to Shia Islam: Up to the 1500s, most Iranian Muslims were Sunni; under the Safavid dynasty, starting with Shah Ismail I around 1501–1502, Iran was forcibly converted to Twelver Shia Islam, shaping its religious identity to this day.

How It Unfolded (In Simple Terms)

  1. 7th century – Conquest phase
    • Arab-Muslim armies fought a series of battles against the Sasanian Empire between about 633 and 651 CE, gradually defeating Persian forces and taking over key cities.
 * The Battle of Nahavand (642 CE), sometimes called the “Victory of Victories,” effectively broke organized Sasanian military resistance and opened the Iranian plateau to sustained Muslim control.
  1. 7th–10th centuries – Slow Islamization
    • Right after the conquest, many people in Iran remained Zoroastrian, Christian, Jewish, or followed other local beliefs; Islam was initially a minority religion among the native population.
 * Over time, through a mix of social influence, intermarriage, economic incentives (like lower taxes for Muslims), and cultural exchange, more Iranians converted, so that by around 950 CE, perhaps 80% or more were Muslim.
  1. 16th century – “Taking over” as Shia Iran
    • In 1501, the Safavid ruler Ismail I seized power and declared Twelver Shiism the official state religion of Iran and neighboring Azerbaijan, enforcing conversion on a largely Sunni population.
 * This Safavid policy is what fixed Iran’s distinct identity as a predominantly Shia Muslim country, different from most of the Sunni Muslim world.

If You’re Asking “What Year Did Islam Take Over Iran?”

You could reasonably point to different milestones depending on what “take over” means:

  • Political takeover:
    • Around 651 CE , with the fall of Yazdegerd III and the collapse of the Sasanian Empire under Muslim rule.
  • Religious majority:
    • Around the 10th century (c. 950 CE) , when the majority of the population appears to have been Muslim.
  • Distinctly Shia Iran:
    • Beginning 1501 CE , with the Safavids’ forcible imposition of Twelver Shiism as state doctrine.

So there is no single date when “Islam took over Iran,” but rather a series of turning points : conquest in the 7th century, majority conversion by the 10th century, and Shia state identity from the early 16th century.

Information gathered from public forums or data available on the internet and portrayed here.