Kugan, 22, was arrested on January 14, 2009, to help in investigations into a luxury car theft syndicate.
He died six days later, triggering uproar among the country's minority ethnic Indian population of police brutality.
Sessions Court Judge Aslam Zainuddin sentenced constable V Navindran, also an ethnic Indian, to three years' jail from the date of sentencing for each count, with the sentences to be served concurrently.
"The defence failed to raise a reasonable doubt in this case," said Aslam.
The judge allowed a stay of execution pending appeal.
Navindran was accused of two alternative counts of causing hurt to Kugan at the interrogation room of the police station on Jan 16, 2009.
A court had acquitted Navindran of the charges but the High Court later overturned the acquittal and ordered him to enter his defence.
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Navindran's lawyer said his client was innocent and had been made a "scapegoat".
The lawyer said he would appeal against the verdict.
Ethnic Indians form about eight per cent of the country's 28 million people.