The 56-year-old judge and cleric registered on Friday for the May 19 vote and his candidacy is being closely watched by foreign investors and diplomats who fear the return of a hardline administration that could threaten the 2015 nuclear deal with world powers and efforts to open up trade.
So far, Raisi has given little indication of his views on foreign policy, keeping his comments vague and predictable.
"Our relations will be ongoing with every country -- except the occupying regime of Israel -- but on condition of respect," he said Friday.
Analysts describe Raisi as utterly loyal to supreme leader Ayatollah Ali Khamenei, meaning he would likely remain deeply suspicious of engagement with the West but unlikely to backtrack on the nuclear deal, which had the boss's tacit consent.
"He has no experience in foreign policy, so at least initially he will have to follow the system's grand strategy of preserving the nuclear deal and shifting any blame of undermining it to the US," said Ali Vaez, Iran analyst for the International Crisis Group.
- Entrenched conservative -
Raisi is entrenched in the conservative establishment, having served as attorney general, supervisor of state broadcaster IRIB and prosecutor in the Special Court for Clerics.
Press reports indicate he has recently been elevated to the status of "ayatollah".
His father-in-law leads Friday prayers in Mashhad and both have seats on the Assembly of Experts that will choose the next supreme leader -- a position for which Raisi himself is often rumoured to be in the running.
There is little chance he will ease social restrictions or release opposition leaders held under house arrest since the 2009 protest movement, known to conservatives as "the sedition".
"The Islamic System has treated the heads of the sedition with mercy. Those who sympathise with the heads of sedition must know that the great nation of Iran will never forgive this great injustice," he said in 2014.
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Crucially, Khamenei picked him in March 2016 to head Astan Qods Razavi -- the centuries-old foundation that looks after the Imam Reza shrine in Mashhad -- placing him at the intersection of political, religious and economic power.
The foundation hosts 20 million pilgrims a year at the shrine, and has also developed into a sprawling, multi-billion-dollar conglomerate that runs everything from farms and power plants to brokerages and IT firms.
- Why is he running? -
One big question is why Raisi would risk a run for the presidency if he has ambitions to become supreme leader as many speculate.
"If he loses, his status will be damaged, so it seems like a big risk," said a Western diplomat on condition of anonymity.
"Moreover, all presidents end up facing criticism from the supreme leader -- that's how the system is set up -- so why put himself in that position?"
The presidency could provide a stepping stone to the top -- as it was for Khamenei in the 1980s.
"But if he loses to the incumbent, who has no rivals in his own camp and has remarkable executive credentials, Raisi's future rise to the peak will be in question," said Vaez.
For now, Raisi has focused on domestic economic issues, playing to the conservative base among poorer, more religious voters.
"Despite four decades of the Islamic system and many promising achievements, people are still suffering chronic problems," he said when announcing his bid last week.
The 12 percent jobless rate and slow trickle down of benefits from the nuclear deal are seen as Rouhani's weak spots.
"Raisi's lifestyle is modest and he regularly stays with the poor sections of society, while Mr Rouhani has more of an aristocratic, comfort-seeking spirit," said Hamid Reza Taraghi, a member of the conservative Islamic Coalition Party.
His opponents are unimpressed.
"Mr Raisi has absolutely no plan to manage the country. Even (former hardline president Mahmud) Ahmadinejad had more experience and he was disastrous for the economy," said reformist Tehran-based economist Saeed Laylaz.