Australian Nguyen Tuong Van was hanged in Singapore three years after his conviction for drug running.
Nguyen, of Vietnamese descent, is the first Australian to be executed overseas in more than a decade.
In the hours before the death penalty was carried out, hundreds of people in Australia and Singapore held a vigil.
A church service was held in his home city of Melbourne. A church bell rang 25 times - once for every year of his life.
In the Australian city of Sydney, people left their offices to join a silent vigil at Martin Place in the financial district.
Nguyen's twin brother Khoa, pictured here in the white cap, joined a vigil at Changi prison where the execution took place.
Australia had repeatedly pleaded for clemency, saying the case had mitigating circumstances.
Nguyen said he smuggled the drugs to earn enough to pay off the legal bills of his brother, an ex-heroin addict.
Human rights activists condemned the execution. Nguyen's family "have been brutalised by this cruel punishment," said Tim Goodwin of Amnesty International.