Stephen Phillip Long, 61, admitted fatally shooting his 24-year-old son Samuel Phillip Long in March this year.
The court heard that while the pair were hunting on Stewart Island, Mr Long had been only 20 metres away from his son when he fired the fatal shot - mistaking him for a deer.
In sentencing him in the Invercargill District Court today, Judge Bernadette Farnan broke down with emotion.
She said Mr Long had shown remorse and been punished enough by the tragedy.
Mr Long's lawyer John Fraser had earlier told the court his client's subconcious mind had taken over his rational mind when he mistook his son for a deer and fired.
Mr Fraser said he did not believe the discharge sent the wrong message about gun safety.
After the sentencing, Mr Fraser said shooting your own family member was probably the most powerful message about gun safety there can be.
"Even if Mr Long had been sentenced to home detention, which was the likely outcome had he not be granted a discharge, I don't think the deterrent message would be any different."