A neighbour tried to save him after alerting the emergency services, but was driven back by the flames, intense heat and thick smoke.
West Sussex Fire & Rescue Service was called to the first floor maisonette in Gratwicke Road in Worthing shortly before 5.15am.
The neighbour raised the alarm after they heard the windows of the converted terraced house blow out.
Two fire engines from Worthing were on the scene within minutes. One team wearing breathing apparatus conducted a search of the property, while a second crew brought the fire under control to stop it spreading to neighbouring properties.
Firefighters found one man on the second floor of the maisonette, but he had already died.
Fire investigation officers are currently at the scene working alongside the police to establish the cause of the fire which is believed to have started in the lounge area of the maisonette.
At this stage there is no evidence to suggest that the fire is suspicious.