Police were called to the inner city suburb of Southbank to reports of a man injured in an apartment building on Sturt Street just after midnight.
The victim was treated by paramedics but died at the scene. He is yet to be formally identified.
A man was arrested nearby and is currently assisting police with their enquiries.
The exact circumstances surrounding the incident are yet to be determined at this stage.
Investigators are not looking for anyone else in relation to the incident.