Maxim Lapunov, who gave a press conference in Moscow, is the first victim to come forward since reports emerged in March of gay men being imprisoned and beaten in the mainly Muslim region where homosexuality is taboo.
The reports prompted international condemnation and German Chancellor Angela Merkel publicly urged President Vladimir Putin in May to investigate.
Lapunov, a 30-year-old ethnic Russian who lived in Chechnya for two years, said he was detained on the street in the main city of Grozny by men in plain clothes and taken to a police station.
There he was imprisoned in a cellar for 12 days and beaten by police who threatened to kill him for being gay, he claimed.
"The main accusation against me was that I'm gay," he said.
The police "would shout that I'm gay, that people like me should be killed."
Lapunov described being thrown into a cell drenched in blood.
"The cell was around two by two metres and about a quarter of the floor was just covered in blood -- it was quite fresh blood," he said.
He believed he would be killed.
"Based on their words and their actions, I thought that after a certain time they would kill me in any case."
Hours after his detention, police began beating him.
"They started beating me with sticks. I don't know how long it took but a very long time," he said.
"They hit me on the calves, they put my face to a wall and beat me on the legs, thighs, buttocks and back, until I started to fall."
Lapunov gave a news conference at Novaya Gazeta, an opposition newspaper which first reported that Chechen authorities were imprisoning and torturing gay men.
"The only thing that I would like now is justice," said Lapunov.
He first came forward in August with the help of the Committee against Torture, a rights group.
His testimony came after Russian authorities initially dismissed the reports, arguing there was no factual basis.
Russian rights ombudswoman Tatiana Moskalkova acknowledged on Friday that she had received a statement from Lapunov.
"I handed his statement to investigative bodies and they are working on it," she said, RIA Novosti state news agency reported.
Lapunov said he was detained from March 16 to 28, before being released on condition that he signed forms, put his fingerprints on a gun and made a video admitting to being gay, he said.
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