The 29-year-old was found seriously injured in the town's Wellington Street, at around 1.15am yesterday after police were called to reports of a disturbance in the area.
A 37-year-old man was also injured as a result of the incident, police revealed.
Both men were taken by ambulance to Inverclyde Royal Hospital, where the 29-year-old later died.
A post-mortem was due to take place to establish the exact cause of his death.
Hospital staff said the second man was currently in a stable condition.
Police want to trace a group of people who officers believe were involved in the incident. A full forensic investigation was under way at the scene.
A blue screen was placed over the entrance of a block of flats in Roxburgh Way and a section of Wellington Street was closed by police.
Detectives were also carrying out investigations in nearby Duncan Street, where an officer was stationed outside flats.
Uniformed officers stood guard at cordons as detectives were seen carrying out their investigations and a police incident support unit was set up at the scene.
Detective Inspector Una Maider, from Police Scotland's Major Investigation Team, who is leading the inquiry, said: "At this time, we believe there were three or four people, involved in the incident."