Four police officers have been acquitted of the offence, prompting anger from human rights groups.
Two men have been convicted of killing prominent LGBT+ activist Zacharias Kostopoulos in Athens in 2018.
A court in Athens found the suspects, aged 59 and 77, guilty of beating and inflicting serious injuries that caused the 33-year-old's death. They were each given a maximum prison sentence of 10 years.
The killing of Kostopoulos -- also known as "Zak" or "Zackie Oh" -- generated widespread outcry in Greece.
The Greek-American national was severely beaten by two men in broad daylight in September 2018. The suspects claimed the LGBT+ activist tried to rob a jewellery shop that one of them owned.
Kostopoulos managed to escape from the shop through a broken window but he was beaten by the men and passers-by on the street outside.
Viral videos on social media showed him being handcuffed by police as he bled on the pavement. He was later pronounced dead in hospital.
LGBT+ communities in Greece argued that Kostopoulos' death was a textbook case of a "hate crime".
Amnesty International had described his death as a "lynching" and "murder", while also criticising the police officers' use of violence.
On Tuesday, four police officers were acquitted of "grievous bodily harm leading to death," prompting angry shouts of "shame" from human rights activists.
The director of Amnesty International’s Greek branch, Glykeria Arapi, said the decision was "yet another example in Greece where victims of unnecessary use of force and their families are left without justice".