NSW Ambulance paramedics performed emergency treatment and CPR on the man in the helicopter and in a cliff-top car park, according to Westpac Life Saver Rescue Helicopter.
But the man, believed to be in his 30s, was unable to be revived, police said.
Police believe he may have been taking photographs at the whale-watching platform before the fall.
The death is not being treated as suspicious, with police believing it was "misadventure".
A spokesman from Westpac Life Saver Rescue Helicopter said the man was found with "significant injuries", possibly indicating "a fall from height".
The man has not yet been positively identified.
Police are on the scene and have launched an investigation.
A report will be prepared for the coroner.
Police examined the cliffs at Kurnell where the man is believed to have fallen.
Photo: 7 News SydneyMore to come