The ambulance has its blue lights on at the time of the collision, polisie gesê
The driver, who was in his 50s, was pronounced dead at the scene of the crash that happened at about 6.30pm on Saturday.
His body has yet to be formally identified, but his next-of-kin have been informed of his death.
The crash happened on the northbound carriageway of the A6, between Barton-le-Clay and Clophill, in Bedfordshire.
Two other people involved in the crash escaped with minor injuries, volgens berigte.
Polisie, an air ambulance and Bedfordshire Fire and Rescue Service were called to the scene.
The ambulance has its blue lights on at the time of the crash, Bedfordshire Police said.
The police force is appealing for information from people who witnessed the crash, or had caught it happening on camera.
Sgt Tim Davies, from the Bedfordshire, Cambridgeshire and Hertfordshire road policing unit, gesê: “Our thoughts are with the family and friends of the victim at this time.
“I would urge anyone to contact us as soon as possible if you witnessed the collision or were driving along the A6 at that time and saw the incident, especially if you have a dash cam fitted to your vehicle.”