Pham Trung Dung, 39, was arrested at Tan Son Nhat Airport in May 2013 when checking in for a flight to Sydney after customs officers suspected he had drugs in his luggage.
He was sentenced to death in April 2014 after police identified the powder as more than four kilograms of heroin.
The Supreme People’s Court later ordered authorities to weigh the heroin afresh, and it turned out there were nearly 3.6 kilograms.
The judges ruled on August 24 that it was “a huge amount” that poses a threat to society.
Dung said he was in Vietnam for a family vacation and a local had asked him to carry the drug to Australia for a fee of US$30,500.
Vietnam has some of the world’s toughest drug laws. Those convicted of possessing or smuggling more than 600 grams of heroin or more than 2.5 kilograms of methamphetamine face the death penalty.
The production or sale of 100 grams of heroin or 300 grams of other illegal narcotics is also punishable by death.