The collision took place on Thursday afternoon on the A470 between Dolgellau and Llanelltyd.
A female patient being carried in an ambulance died after a crash which also involved a council lorry.
The drivers of both vehicles were also injured in the crash, which saw the road closed in both directions for several hours.
A spokesman for North Wales Police said: "Sadly a woman has died following a road traffic collision on the A470 in Meirionnydd.
"At 13:12pm, police were notified of a two-vehicle collision involving a tipper van and a Welsh Ambulance Service Non-Emergency Patient Transport Service vehicle near Talrafon, between Dolgellau and Llanelltyd."
He said the emergency services were called to the scene and three people were treated and taken to hospital.