Haig Arslanian was older than 31-year-old David but a court heard he was the smaller brother and afraid of the man he killed.
A Victorian Supreme Court jury found him not guilty of murder in July but was unable to reach a unanimous decision on a separate charge of manslaughter.
A fresh judge-alone trial was run before Justice Rita Incerti. She will deliver her verdict and reasons in the case on Thursday morning.
A number of family members were in court for the verdict.
David Arslanian was shot and killed at the Geelong family home he shared with Haig and their parents in October 2020.
Haig Arslanian, then 39, admits he is to blame for his brother's death and that he fired the gun that ended David's life.
His lawyers successfully argued against the murder charge on the grounds that he was acting in self defence.
They claimed the October 5 shooting was necessary to prevent Haig being killed or seriously injured himself.
In the earlier trial, jurors were told there was frustration, anger and resentment between the brothers, who were no strangers to arguments and fights.
Haig believed David was using hard drugs and gambling, and understood he had stolen money from him and other family members.
In the weeks before the shooting Haig believed he was going to die when David tried to strangle him, his lawyer said.
At 190cm tall and about 170kg, David was substantially bigger than Haig.
The court heard Haig was scared of his brother, a fear which stemmed from a history of David's violence toward him.
On the night of the shooting, Haig had his head pushed through a mirror by David and responded by going for a shotgun stolen from his father's gun safe.
Haig told police afterwards that even with the gun in his hands David had continued to come at him and taunt him.
He said he hadn't intended to shoot David but to scare him off.
Justice Incert's reasons for her verdict are expected to be lengthy.
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