The cleric and former chief justice’s inauguration comes as the country struggles to revive a sanctions-hit economy and restart stalled nuclear talks.
Iranian ultraconservative cleric Ebrahim Raisi has been sworn in as the Islamic republic's eighth president, in a parliamentary ceremony broadcast live on state television.
"I will dedicate myself to the service of the people, the honour of the country, the propagation of religion and morality, and the support of truth and justice," Raisi said on Thursday.
Raisi, 60, was inaugurated two days after winning the formal endorsement of the country's supreme leader to take office following his victory in an election in June.
Raisi, who is under US sanctions over allegations of human rights abuses when he was a judge, has promised to take steps to lift tough American sanctions that have cut Iran's oil exports and have shut it out of the international banking system.
Iran has been negotiating with six major powers to revive a 2015 nuclear deal abandoned three years ago by then US President Donald Trump.
Under the deal, Iran agreed to curb its nuclear programme in return for the lifting of international sanctions, but Trump withdrew from the deal and reimposed sanctions that have crippled Iran's economy.
Tehran has since breached limits imposed on its nuclear activities under the agreement.
Like Iran's supreme leader, Raisi has endorsed the nuclear talks, but the mid-ranking Shia cleric is widely expected to adopt a tougher line in talks that have stalled.
A dark past
A former chief justice, Raisi’s victory in the election was viewed as controversial by many observers. Rights groups say he was involved in the 1988 mass executions.
His June 19 win at the presidential race was widely anticipated after many political heavyweights were barred from contesting the polls.
Soon after his win Human Rights Watch lashed out at the Iranian political establishment for holding an "unfair election" and paving the way for Raisi to become president while other rights groups dug up his murky past.
For Maryam Rajavi, President-elect of the Paris-based National Council of Resistance of Iran, Raisi is the henchman of the 1988 massacre.
Raisi was among the panel of judges who were involved in ordering mass executions of political prisoners in the summer and fall of 1988. Known as one of the most tragic incidents in Iran’s post-revolution history, the judgements led to the hangings of thousands of prisoners.
According to a UN report released in 2017, Iranian government massacred 30,000 political prisoners based on a fatwa by the first Supreme Leader of the Revolution, Ayatollah Khomeini.
Raisi’s victory was also overshadowed by a historic low turnout for a presidential election as only 48.8 percent of the more than 59 million eligible voters turned up to vote.
Prior to his presidential run, Raisi was appointed as Chief Justice of the country in 2019 by Supreme Leader Ayatollah Ali Khamenei.
Born in a clerical family in the Noghan district of Mashhad, a place famous for religious pilgrimages, Raisi holds a masters degree in the field of International Private Law and a PhD in "jurisprudence and fundamentals of Islamic law" from Shahid Motahari University.
His religious education in Qom established his clerical credentials, one of the premier places of learning for Shia scholarship, and he was also the student of many famous Shia scholars.
After the Iranian Revolution in 1979, he served as a prosecutor in several cities in Iran.
In 1981, he started his career by becoming the prosecutor of Karaj, located 20 kilometre west of Tehran. Afterwards, he was also appointed for the same role in Hamadan and carried out his active roles in two cities more than 300 km away from each other.
In 1985, he was appointed deputy prosecutor of Tehran and in 1989, promoted to the post of senior prosecutor in the capital.
In 2014, he was appointed Attorney-General of Iran, a position he held until 2016.
Raisi lost the 2017 presidential election to current President Rouhani as a candidate for the Popular Front of Islamic Revolution Forces (JAMNA) and supported by other revolutionary factions.