Victoria’s Court of Appeal on Monday ruled that, after “anxious consideration”, his sentence should be cut by 18 months.
The 12-year sentence he was handed for manslaughter and the six years for attempted murder were appropriate, they said.
But ordering Vu serve three years of the attempted murder sentence on top of the manslaughter sentence was too much they said, reducing it to 18 months.
Vu will now serve up to 13-and-a-half years behind bars and will be eligible for parole after a decade.
The appeal court said manslaughter ranged from a joke gone wrong to just short of murder.
“This is a manslaughter verdict that can legitimately be characterised as just short of murder,” they said.
Vu was charged with murder, but a jury convicted him of the lesser offence.
He had first started a relationship with Ms Chan in the early 2000s and was living with her at the time of the attack.
Ms Chan began a relationship with Mr Nguyen while Vu was in prison over a drug related offence.
The men became friends after Vu’s release, but Vu confronted Mr Nguyen in a heated exchange after learning he and Ms Chan had married secretly.
Ms Chan gave a statement of support for Vu when he was sentenced initially, but Justice Andrew Tinney said the crime “must have been a very traumatic event for her”.