The protests, which reportedly spread to 180 cities and towns in all 31 provinces, were sparked by anger over the collapse of the Iranian currency and soaring cost of living.
They quickly widened into demands for political change and became one of the most serious challenges to the clerical establishment since the 1979 Islamic revolution.
While a near total shutdown of the internet and communication services made it difficult to find out what was happening in the country, protesters told the BBC the lethal crackdown by security forces was unlike anything they had witnessed before.
According to the US-based Human Rights Activists News Agency (Hrana), at least 7,000 people were killed in the January crackdown, including 6,488 protesters and 236 children.
US President Donald Trump said in January that “strong action” would be taken against Iran if protesters were executed. Iranian Foreign Minister Abbas Araghchi said afterwards that there was “no plan” to hang people.
One protester, Erfan Soltani, who had been arrested on 8 January and whose family had been told would be executed within days, according to the Norway-based Kurdish human rights group Hengaw, was later reportedly released on bail.
Iran’s judiciary denied he had been sentenced to death, saying he faced security-related charges carrying prison terms only.
Since then, the US and Israel have launched wide-ranging strikes on Iran, killing the country’s supreme leader. Iran has responded by launching attacks on Israel and US-allied states in the Gulf.