The two main rivals in the race are widely expected to be President Hassan Rouhani, and Ebrahim Raeesi.
Iranian President Hassan Rouhani has registered to run for a second four-year term in the country's election in May.
He has made much of his successes in controlling inflation and reaching a landmark nuclear deal with world powers that ended many sanctions.
He is the custodian of a powerful organisation in charge of Iran's holiest shrine.
"The people's vote will determine the country's fate".
"From now on, protecting the deal is one of the most important economic and political issues", said Rouhani.
Ellie Geranmayeh, a senior policy fellow for the Middle East and North Africa program at the European Council for Foreign Relations, told Bloomberg that despite sanctions against Iran being lifted, "people are not seeing a huge elevation for Iran in terms of the economy or its place on the global stage".
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Rouhani, a politically moderate cleric, inherited an economy in freefall and a country dangerously isolated over its nuclear programme when he took power in 2013.
Rouhani, who won the 2013 presidential elections in the first round with 50.8 per cent of the vote, is the candidate of the reformist bloc, although he defines himself as moderate.
After the registration, Raisi called for "respect to the law" by both people and the officials.
Ultimate authority rests with Supreme Leader Ayatollah Ali Khamenei, who has accused the West of using women as a tool to advertise products and satisfy "disorderly and unlawful sexual needs".
He was also Prosecutor and Deputy Prosecutor of Tehran in 1980s and 1990s. He is also a member of Assembly of Experts, an all-cleric body that will rule on the successor for the Supreme Leader.
His reelection in 2009, marred by fraud allegations, led to the biggest protests in Iran since the 1979 revolution."I merely registered here to support my dear brother, Baghaei", Mr. Ahmadinejad said, referring to Hamid Baghaei, his former vice president.