Amnesty International says Iran arrested 7,000 people last year in a "shameless campaign of repression".
Those swept up by the crackdown included protesters, students, lawyers, journalists, environmental and women's rights activists, and trade unionists.
Hundreds were sentenced to prison or flogging. At least 26 protesters were killed and nine others died in custody.
The crackdown was a response to unrest over poverty, corruption and the lack of political and social freedoms.
"From underpaid teachers to factory workers struggling to feed their families, those who have dared to demand their rights in Iran today have paid a heavy price," said Philip Luther, Amnesty's Middle East and North Africa director.
Women's rights defenders
Amnesty said at least 112 were arrested or remained in detention during 2018, when women began standing on raised structures in public places and taking off their headscarves to protest against the compulsory hijab law.
The prominent human rights lawyer Nasrin Sotoudeh, who defended women arrested over the protests, was herself arrested in June and faces several national security-related charges. Ms Sotoudeh's husband Reza Khandan, who had campaigned for her release, was jailed for six years on Wednesday.
At least 63 activists and researchers were reportedly detained in 2018.
Without providing evidence, the authorities accused a number of them of collecting classified information about Iran's strategic areas under the pretext of carrying out environmental and scientific projects, according to Amnesty.
Five activists - Morad Tahbaz, Niloufar Bayani, Houman Jokar, Sepideh Kashani and Taher Ghadirian - were charged with "corruption on earth", a capital offence.
Workers and trade unionists
Iran's deepening economic crisis - the result of sanctions reimposed by the United States, government mismanagement, and corruption - triggered strikes and protests by people demanding better working conditions and higher wages.
At least 467 people, including 23 teachers, lorry drivers and factory workers, were arrested and dozens were sentenced to prison. Thirty-eight people got lashes.
Amnesty said more than 200 members of Iran's largest Sufi Muslim order, the Gonabadi dervishes, were sentenced to prison and lashes after taking part in peaceful protests that were violently suppressed by security forces in February.
One man, Mohammad Salas, was executed in June after being convicted of the murder of three policemen who were run over by a bus at a protest. Amnesty said a witness who provided him with an alibi was not allowed to testify at his trial.
At least 20 were handed long prison or flogging sentences after what Amnesty said were unfair trials.
Mohammad Hossein Sodagar, a journalist from the Azerbaijani Turkic ethnic minority, was given 74 lashes after being convicted of "spreading lies".