In the 57kg category 2020 Olympic qualifiers in Jordan, he first surprised Australian Charlie Senior to reach the quarterfinals.
He then needed to beat Thailand's Chatchai Decha Butdee to win a ticket to Tokyo since six qualifiers were to go through.
Butdee had beaten Duong in the SEA Games finals last year, but it was sweet revenge for the Vietnamese this time as he was declared winner in just 60 seconds.
Duong started dominantly, throwing powerful left jabs which left the Thai boxer stunned. The referee awarded the win to Duong after he floored Butdee twice.
He is the second Vietnamese boxer to qualify for Olympics, after Dang Hieu Hien entered 1988 Olympics in Seoul.
The 24-year-old boxer said: "I lost to Butdee in the SEA Games 30 final, and so I felt happy that I had the chance to take revenge here. It’s even better since this victory has taken me to the Olympics."
The aggressive fighter has won the national title three times in this weight category.
Vietnam so far has five athletes in this year’s Olympics in swimming, gymnastics, archery, and boxing. The target set by the country is 20.