The incident happened near Heathrow Airport between junctions 14 and 15 just after 9.30am today (March 18).
Officers and London Ambulance Service crews attended, and CPR was performed on the driver of the van.
He was pronounced dead at the scene shortly after.
The driver of the truck did not suffer any serious injuries.
No arrests have been made following the incident.
The incident caused severe delays in the area but traffic has since returned back to normal.
A spokesperson for Metropolitan Police said: “Police were called to the scene of a collision between a lorry and a van on the Clockwise M25, between J14 and J15, on Monday 18, March at 0934hrs.
“Officers attended along with London Ambulance Service paramedics, who performed CPR on the driver of the van, a man believed to be in his 70’s.
“Despite their best efforts the man died at the scene.
“The driver of the truck did not suffer any serious injuries.
“No arrests have been made.
“Any witnesses or those with dash cam footage are asked to call 101 or tweet @MetCC quoting CAD 2484/18MAR.
“Alternatively, to remain 100% anonymous please contact the independent charity Crimestoppers on 0800 555 111.”
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