Silviu Ionescu, Romania's charge d'affaires in Singapore at the time, was initially sentenced to three years behind bars after being found guilty of manslaughter for hitting three pedestrians in December 2009 while driving a car belonging to the Romanian mission.
One of the pedestrians, a 30-year-old Malaysian, died.
The appeals court also found him guilty of inflicting injuries and fleeing from the location of the crash, according to the ruling.
His lawyer was not immediately available for comment.
His defence team argued during the trial that he should be acquitted on the grounds that there was no direct evidence linking him to the crime.
Ionescu fled Singapore shortly after the accident.