Nguyen Ngoc Diep was singing a song to the couple when another guest ridiculed his performance and snatched away the microphone, Tuoi Tre newspaper said.
After a quarrel, Mr Diep went home to return with a knife later that evening.
He injured the man who had mocked him and fatally stabbed another guest who tried to separate them.
The man died later in hospital in Tien Giang province where the incident occurred. Mr Diep has since been arrested, according to the Tuoi Tre newspaper.
In rural areas wedding parties can last for as long as three days with food, heavy drinking and entertainment like karaoke.
Karaoke-related fights are very common in general in Vietnam, though they usually break out over taking turns at singing or splitting the bill, says BBC Vietnamese's Linh Nguyen.
In early May, a man stabbed his friend to death over a dispute during karaoke. Two weeks ago, a man was killed after trying to get customers to pay their karaoke bill.
A row over a karaoke performance has left one dead and another injured at a wedding in southern Vietnam, local media said.