Emergency services were called to a house in Blacktown about 4pm, which was engulfed in flame as they arrived.
Firefighters at the scene were told that there could be a man inside the burning house.
The man was found and brought outside where responders started to perform CPR.
He was treated by paramedics but died at the scene despite their efforts.
He has not yet been formally identified.
NSW Fire and Rescue Superintendent Grant Rice said firefighters were working to stop the fire spreading beyond the property where it started.
“It’s classified as a hoarders’ premise, so they’re doing their best to make sure it doesn’t escalate and extend beyond that property,” Rice said.
Approximately 32 firefighters and eight trucks were called to the scene.
Police were called to the scene for traffic management.