A man who rose quickly through the ranks after Iran's 1979 Islamic revolution, Raisi was accused by activists of overseeing mass executions of prisoners in 1988 followed by a litany of human rights abuses as judiciary chief and later president.
"Ebrahim Raisi was a symbol of judicial impunity for criminals and the entrenched lack of accountability within the Islamic republic's system," Mahmood-Amiry Moghaddam, director of Norway-based group Iran Human Rights, said in a statement to AFP.
He "should have been prosecuted for crimes against humanity and held accountable in a fair trial for the countless atrocities he committed over these four decades," Moghaddam added.
Shadi Sadr, co-founder of the Justice for Iran group, which campaigns for accountability for Iranian rights violations, condemned the condolences offered by some Western figures, including EU Council President Charles Michel, for the deaths of Raisi and his foreign minister Hossein Amir-Abdollahian.
"Such actions are perceived as a betrayal by the countless victims of human rights abuses, deepening the disappointment among the Iranian population towards the international community," she told AFP.
'Crimes against humanity'
Rights groups including Amnesty International have long accused Raisi of having served on a four-man "death committee" that approved the executions of thousands of political prisoners, mostly suspected members of outlawed rebel group the People's Mujahedin of Iran (MEK), in 1988.
Raisi, seen before his death as a possible successor to supreme leader Ayatollah Ali Khamenei, flatly denied personal involvement while praising the decision to go ahead with the executions.
In September 2020, a group of seven UN special rapporteurs wrote to the Iranian government pressing for accountability over the killings, saying "the situation may amount to crimes against humanity".
Maryam Rajavi, the leader of the MEK's political wing the National Council of Resistance of Iran, said that "the curse of mothers and those seeking justice for the executed, along with the damnation of the Iranian people and history, mark the (president's) legacy".
Raisi was promoted to Tehran chief prosecutor in 1989 and deputy head of the judiciary in 2004, a position he held for a decade including during a crackdown on mass protests in 2009.
He became head of the judiciary in 2019 and president in 2021. In 2022, his administration implemented a harsh crackdown on women-led protests that left hundreds dead, according to rights groups.
An independent UN fact-finding mission earlier this year found that Raisi's administration had committed crimes against humanity through its "violent repression" of protests and discrimination against women.
'Pillar of system'
"Sympathy with him is an insult to his victims and the Iranian nation whose only regret is that he did not live long enough to see the fall of the Islamic republic and face trial for his crimes," said Reza Pahlavi, the son of Iran’s ousted shah and a leading opposition figure in the diaspora.
Recent weeks have seen Iranian authorities ramp up enforcement of the mandatory dress code for women, a main focus of the 2022 protests which were triggered the death in custody of Mahsa Amini following her arrest for an alleged breach.
"Raisi was a pillar of a system that jails, tortures, and kills people for daring to criticise state policies," said New York-based Center for Human Rights in Iran executive director Hadi Ghaemi.
"His death has enabled him to escape being held accountable for his many crimes and the state's atrocities committed under his rule."
Ghaemi warned that as Iran's supreme leader seeks to ride the shock to the system of Raisi's sudden loss, there is a risk of a new crackdown on civil society.
"What is crucial now is that the international community must not allow the Islamic republic to exploit this moment to further repress and brutalise the Iranian people," he said
