Faalau Pisu, 23, was shot at least once in the head as he left the reception at a Serbian function centre at Canley Vale shortly after midnight.
He was taken to Liverpool Hospital in a critical condition.
His family made the decision on Monday morning to turn off his life support, the Seven Network said.
Two other men injured in the shooting were taken to hospital in a stable condition – a 27-year-old who is believed to have been shot in the leg and a 25-year-old with minor wounds.
About 50 of Mr Pisu’s grieving relatives gathered at the hospital where police were on guard amid fears of further violence, according to Seven.
It’s been reported that Mr Pisu was a cousin of the groom.
His sister Faimai Faye Ale said her brother would be badly missed.
“Faalau was the best guy. He was a guy with a big heart and he loved each and every one of us, especially the children,” she told ABC radio.
“He went this morning and our family’s really hurt at the moment.
“We love you Faalau and we wish this didn’t happen to you.”
According to his MySpace page, Mr Pisu was an amateur boxer and was studying to become a personal trainer.
He graduated from Ashcroft High School in southwest Sydney in 2006.
Shocked guests spilled out on to Bareena Street after the shooting at the Serbian National Defence Council function centre.
Police were speaking to them on Monday morning.
A man wearing Comanchero bikie colours was spotted among the crowd at the hospital, Fairfax radio reported.