The news prompted an outcry from some Western governments and activists, who feared the execution could be the first of many as the regime violently cracks down on the demonstrations.
Mohsen Shekari was one of 11 people known to have been sentenced to death in relation to the protests, which have posed the biggest challenge to the Islamic Republic's ruling clerical establishment since it came to power in the 1979 revolution.
He was hanged after he was convicted of "waging war against God" — specifically blocking a Tehran street and injuring a pro-regime Basij militia member with a machete — the Mizan news agency, which is run by the judiciary, reported early Thursday.
It said he was tried by Tehran’s Revolutionary Court, which has been criticized internationally by human rights groups for holding opaque show trials in which defendants are not allowed to see the evidence against them.
The regime has been using violent tactics on the streets in an attempt to suppress anti-government protests that have caused upheaval for almost three months.
The unrest broke out in mid-September when a young woman, Mahsa Amini, died in a hospital three days after being arrested by the country's morality police for allegedly breaking the strict dress code.
At least 475 people have been killed and 18,000 others arrested, according to the Washington area-based watchdog group Human Rights Activists in Iran. Iran’s Interior Ministry said Saturday the death toll was 200, including security forces who were killed.
Thursday's news has been met with horror by activists, who condemned the lack of transparency in Shekari's case and feared it could be the first in a string of executions. It "must be met with STRONG reactions otherwise we will be facing daily executions of protesters," Mahmood Amiry-Moghaddam, the director of the Oslo-based activist group Iran Human Rights, said in a tweet.
He called it a "show trial without any due process" and said there needed to be "rapid practical consequences" internationally, without specifying what steps he wanted taken.
"Mohsen gave his life for freedom. He wanted a normal life. One more brave soul killed by this bloody regime," Masih Alinejad, a journalist and activist living in Brooklyn, tweeted.
German Foreign Minister Annalena Baerbock tweeted that Iran’s “contempt for humanity” was “boundless.” She condemned the legal proceedings as a sham trial but warned the regime that “the threat of execution will not suffocate people’s desire for freedom.”
British Foreign Minister James Cleverly posted that he was “outraged” by the news. “The world cannot turn a blind eye to the abhorrent violence committed by the Iranian regime against its own people,” he said.
Shekari was arrested Sept. 25 in Tehran's Sattar Khan district, according to the Mizan news agency, which said he blocked the street, held a machete given to him by a friend, and injured a militiaman, who it said needed 13 stitches.
The news agency alleged that Shekari was offered money to wield the machete and take part in the protests. Iranian officials have for months been seeking to allege, without offering evidence, that foreign states have been behind the unrest, rather than Iranian citizens angry over the country's issues.
No details of the case have been confirmed outside of the information given by Iran's authorities. Amnesty International and other human rights groups say the authoritarian country holds "unfair trials" and uses death sentences by hanging as "a weapon of repression against protesters, dissidents and ethnic minorities."
Iran executed 314 people last year, the most in the world after China, according to data compiled by Amnesty.