The incident happened on the coast-bound carriageway near junction 9 at Ashford shortly before 1pm yesterday (January 23).
Officers and South East Coast Ambulance Service crews attended and a woman was found injured.
However, she was pronounced dead at the scene shortly after.
The west-bound carriageway re-opened at around 2.30pm, the coast-bound carriageway remained shut throughout the afternoon.
The carriageway was fully re-opened at around 11pm and residual delays cleared soon after.
A spokesperson for Kent Police said: “Kent Police was called to a report of a collision involving a pedestrian and a lorry near J9 of the M20 coast-bound at Ashford shortly before 1pm on Thursday, January 23.
“Emergency services attended and the pedestrian was pronounced deceased at the scene.
“Formal identification has yet to take place but the family of a woman in her twenties have been informed.
“Officers are preparing a report for the coroner.”
