How did the 1979 Iranian Revolution change Iran's system of government?

The 1979 Iranian Revolution fundamentally transformed Iran from a monarchy under the Pahlavi dynasty into a theocracy known as the Islamic Republic.123

The new system of government was based on the theory of velāyat-e faqīh ("governance of the jurist"), formulated by Ruhollah Khomeini. Key changes included:13

• Centralization of Power: The constitution established the office of the supreme leader (rahbar), who oversees virtually all government functions and holds sweeping authority over policy and the electoral process.423
• Clerical Oversight: While the country maintains democratic elements like an elected president and parliament, these are constrained by clerical bodies such as the Council of Guardians, which vets candidates and legislation to ensure compliance with Islamic law.42
• Institutional Changes: The government transitioned to a presidential system, and the post of prime minister was abolished in 1989. Additionally, the Islamic Revolutionary Guard Corps was created as a powerful military branch accountable directly to the supreme leader.21
• Social Enforcement: The state moved to enforce conservative social values, including strict codes of dress and public conduct, often through revolutionary committees and militias.13