Majidreza Rahnavard was publicly hanged in Mashhad on Monday after being charged with “moharebeh”, or enmity against God, the judiciary's Mizan news agency said. It later published images of his body hanging from a crane.
He was accused of killing two security officers in the city and trying to flee the country before his arrest.
Activists said his mother was allowed to visit him before his death but was not informed he was going to be executed.
Iran's judiciary has published detailed accounts and photographs of the alleged crimes and trials of people arrested during the protests but has been widely condemned for its legal process, in which dubious charges are pressed with little evidence, often without representation for the accused.
It has vowed to prosecute protest-related cases in the “shortest time possible”.
Detainees are reported to have been tortured into giving forced confessions at closed-door hearings.
More than 18,000 people have been arrested since anti-government demonstrations began in September, according to estimates from human rights groups. Activists have said a dozen more people are at imminent risk of execution.
Mohsen Shekari, accused of wounding a member of the Basij paramilitary force that has led the government's bloody response to the protests, was the first person to be executed.
He was hanged and then buried amid a heavy security presence in the capital.
Five people were sentenced to death last week over the death of a Basij member in the western city of Karaj. The Tehran regime, which has one of the highest execution rates in the world, has defended its capital punishment as “just”.
About 500 people have been killed during nearly three months of nationwide protests, which Tehran describes as “riots”, that were triggered by the death of a young woman, Mahsa Amini, days after she was arrested by morality police in Tehran.
Head of Iran Studies at the Emirates Policy Centre (EPC), Mohamad Al Zghool, said the recent executions have worsened the continuing protests and exposed deeper rifts among pro-government figures.
"This is a Gen Z protest that the Iranian government thought it could quash by limiting internet and social media access among demonstrators who are not calling for reform of the regime, but its total removal."
"Internal struggles, too, within the country, reveal that some clerics are unhappy with the executions as a punishment, arguing that they do not fit the crime."
One such official is Sunni-Baluchi cleric Molavi Abdolhamid, who has spoken out against the death sentences.
"When someone has not killed but only blocked a road and stabbed and injured a Basij (militia) member with a knife, he cannot be put to death under Sharia," he said.
"This protest will not be quelled by killing people."
Despite such instances of dissent, Mr Al Zghool does not think the Iranian regime is on the verge of collapse.
"I think the government will be unable to resolve this issue like it did with earlier problems, but the nucleus of the regime is still very strong. So while I don't think that the regime is going to collapse in the next few years, I do think that Iran is on the path to becoming a failed state," he said, citing the example of Syria, which despite an 11-year war is still led by President Bashar Al Assad today.
Iran's continuing crackdown on the protests, which has drawn international condemnation, comes as its currency, already weakened by progressive rounds of western sanctions, has dropped to a new low against the US dollar.
The rial was trading at 370,000 to the dollar on Sunday, compared with 368,000 on Thursday, continuing a slide over recent months as efforts to revive its 2015 nuclear deal with world powers stalled.
Its currency was trading at 32,000 rials to the dollar at the time of the accord, which dropped international sanctions in exchange for tight controls on Iran’s nuclear programme. The deal began to fall apart in 2018 after Donald Trump, US president at the time, pulled Washington out of the deal and reimposed sanctions on Tehran.
Last week, the US imposed sanctions on a Turkish businessman for arranging oil sales and laundering money for Iran's Islamic Revolutionary Guard Corps.
New sanctions expected
Iran has also been hit with western sanctions for supplying drones to Russia that have been used in Moscow's attack on Ukraine. The European Union was preparing to impose new sanctions on Monday that the bloc's foreign policy chief, Josep Borrell, said would be “very tough”.
Speaking ahead of the EU Foreign Council meeting, German Foreign Minister Annalena Baerbock said Iran's executions are a “blatant attempt to intimidate protesters.”
Canada imposed sanctions on Iran on Friday over its drone supplies and human rights abuses.
“Canada will not stand idly by while the regime’s human rights violations increase in scope and intensity against the Iranian people,” said Foreign Affairs minister Melanie Joly.
The Canadian move was followed by a New Zealand travel ban on Iranian security forces.
“What happened to Mahsa Amini is inexcusable. New Zealand continues to stand with the people of Iran, especially women and girls,” Prime Minister Jacinda Ardern said.
IRGC commander Hossein Salami and the leaders of the Basij and morality police are among the 22 people now banned from travelling to or through the island nation.
UK's Foreign Secretary James Cleverly said Westminster would “try to steer Iran in a better direction” and continue to “respond when Tehran's actions are unacceptable”.
Recent sanctions over Iran's drone sales and its human rights abuses are the latest in a long line of measures handed down on Tehran since the breakdown of the nuclear deal.
Protesters have urged the US to give up attempts to revive the accord, saying that it lends legitimacy to the regime.
Iran has stepped up its nuclear agenda since the US withdrawal from the accord, vowing to resist Washington's “maximum pressure” sanctions.
It has increased its stockpile of highly enriched uranium to one step below the level required for producing a nuclear bomb, and has resisted the UN atomic agency's demands to explain the presence of enriched uranium at three undeclared sites.
Saudi Arabia warned on Sunday that “all bets are off” if Iran obtains a nuclear weapon.
“We are in a very dangerous space in the region … you can expect that regional states will certainly look towards how they can ensure their own security,” Saudi Foreign Minister Faisal bin Farhan said at the World Policy Conference in Abu Dhabi.
The diplomatic adviser to the UAE's President Sheikh Mohamed echoed the danger Iran posed to the region, calling for “explicit” security reassurances from the West.
European ties with the Gulf “should not be transactional”, said Dr Anwar Gargash, adding that Iran's drone supply called for the nuclear deal to be “revisited”.
Western co-operation must be long-term and strategic, Dr Gargash said.