The UN Human Rights Council has decided to conduct an independent investigation into the ongoing violence by the Iranian security apparatus against demonstrators.
Experts should document violations of human rights and collect evidence so that those responsible for the violence can one day be held accountable, as Foreign Minister Annalena Baerbock (Greens) said in Geneva.
Germany and Iceland had submitted a corresponding resolution.
The Council of 47 countries voted in favour, 25 to 6, with 16 abstentions.
The high number of approvals exceeded all expectations in Western countries.
Applause erupted in the hall after the vote.
Baerbock had come specifically to give a voice to the thousands of people in Iran who are committed solely to a life of dignity and without discrimination, as she said.
The world should not stand by and watch "innocent people, mothers, fathers, sisters, brothers and children being murdered." China tried at the last minute to remove the paragraph that called for an independent investigation from the resolution.
The Council voted against by a large majority.
The UN High Commissioner for Human Rights, Volker Türk, spoke of a tyranny in Iran.
According to his office, more than 300 people have died since the protests began in mid-September.
He called for the release of more than 14,000 people arrested in connection with protests.
Participants and journalists would be labeled "agents of enemies and foreign states".
That is the typical narrative of tyranny.
A representative of the Iranian government criticized the western states as arrogant hypocrites.
They are violating the human rights of Iranians through the sanctions, which have claimed many lives, said Khadijeh Karimi, deputy vice-president for women and family affairs.
A diplomat from Iran claimed before the vote that the "German regime" and security forces were repressing even peaceful protesters in Berlin, Stuttgart and elsewhere demanding more social justice.
Human rights leave no room for interpretation, Baerbock said.
The right to freedom of expression is guaranteed and also applies in Iran.
"The Human Rights Council was created to be the voice of the people whose indivisible rights are being denied in their own homes," she later told reporters.
"When the right to sovereignty is abused to oppress one's own people and thereby also trample on the Charter of the United Nations, the United Nations must raise its voice."
The image of a little Iranian girl kneeling in the dust by her mother's coffin screaming at the sky gets under her skin, Baerbock said.
She herself has been to many demonstrations, sometimes with prams.
In democratic countries, it goes without saying that you can come home safely afterwards.