Nagaenthran Dharmalingam, 34, had been on death row for more than a decade for trafficking 44 grams (1.5 oz) of heroin into Singapore, which has some of the world's toughest narcotics laws. His lawyers had filed multiple appeals against his execution saying he was intellectually disabled.
His brother Navin Kumar, 22, said by telephone the execution had been carried out and said the body would be sent back to Malaysia where a funeral would be held in the town of Ipoh.
A Singapore court on Tuesday had turned down a legal challenge put forward by Nagaenthran's mother, clearing the way for the execution by hanging.
At the end of Tuesday's hearing, Dharmalingam and his family reached through a gap in a glass screen to grasp each others' hands tightly as they wept. His cries of "ma" could be heard around the courtroom.
About 300 people held a candlelight vigil at a Singapore park on Monday to protest against the planned hanging.
Nagaenthran's case has attracted world attention, with a group of United Nations experts and British billionaire Richard Branson joining Malaysia's prime minister and human rights activists to urge Singapore to commute his death sentence.
His lawyers and activists have said Nagaenthran's IQ was found to be at 69, a level recognised as an intellectual disability. However, the courts determined he knew what he was doing at the time of his crime, and ruled there was no admissible evidence showing any decline in his mental condition._Reuters
The Singapore government says the death penalty is a deterrent against drug trafficking and most of its citizens support capital punishment.
