Michel Francoise Theodoor Willemyns hit and stomped on his brother so hard his sibling's skull was fractured.
Then he videoed himself talking to the severely injured, groaning man.
Before their mother's death the previous year the men had a close, loving relationship.
But by March 5, 2017, it had deteriorated into arguments and physical fights, a court judgment says.
Arriving at his brother's unit in Karana Downs, west of Brisbane, about 9pm Willemyns watched from outside while swinging a metal spanner he had brought wrapped in cloth.
He smashed a glass panel to get inside then hit Patrick Pierre Willemyns on the head with the spanner.
When his brother tried to get up from a sofa, Willemyns again hit the back of his head before stomping on him over a period of time.
Willemyns videoed himself talking to his severely injured brother who just groaned in response.
About eight hours after Willemyns left the unit with his brother's laptop, the body was found on the sofa with a large amount of blood on the floor and furniture.
Willemyns admitted the attack, saying he was angry and believed his brother had stolen money and his passport.
"He said words to the effect that he wanted to kill the monster inside his brother," Appeal Court Justice Peter Flanagan said in the judgment published on Friday.
Willemyns claimed his brother was breathing and lucid, although injured, when he left the unit about 5am.
The sentencing judge found that hard to accept but if true it made the crime even more horrific due to the extent of the injuries.
But Willemyns had a mental illness that substantially impaired his capacity to know he ought not to do what he did, she said.
Willemyns was originally charged with murder but pleaded guilty in September to manslaughter.
He applied to appeal his 10-year jail term saying the sentencing judge failed to take into account his mental health.
Queensland's Court of Appeal sitting in Brisbane dismissed the application, finding Willemyns' proposed grounds did not have merit.
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