Emergency services were called to Fletcher Street in Tamarama, near Bondi, about 4am, where he was found critically injured.
Despite attempts to resuscitate him, he was unable to be revived.
A crime scene has been established as police and crash scene investigators are combing through the site.
Detective Acting Superintendent Adam Solah said the man was believed to have been a pedestrian killed in an alleged hit-and-run.
“The family are obviously very upset and distraught and our hearts go out to them,” he said at a press conference today.
Solah said the man was believed to have been local to the area and appealed to the public for any information, dashcam or CCTV footage to contact police.
“He is described as a 28-year-old male, slim build, Caucasian background, brown hair, he’s wearing a blue button up shirt and tan shorts,” he said.
The alleged driver behind the hit-and-run was also urged to come forward.
Fletcher Street between Glen and Silver streets has been cordoned off with drivers urged to avoid the area.