Police and paramedics were called to a picnic area on the Duckholes Trial in Terry Hills, which is part of the national park, at 12.30pm.
The man reportedly fell 20 metres from the cliff into the water below.
The body of the man, believed to be in his 40s, has been recovered from the water by firefighters, who were roped down to the site and pulled the man’s body up.
FRNSW Superintendent Adam Dewberry called the scene “confronting.”
“He was with a group of people, a lot of young people as well who have witnessed this.
“[Firefighters] were able to get him onto the rocks but, unfortunately… despite best efforts, he could not be revived.
“[It’s a] really confronting situation for everyone involved. [It’s also] a really dangerous situation, particularly for our firefighters who were on rope… to get down and recover this man.”
The victim has not yet been formally identified.
The national park had to be evacuated while emergency operations were underway.