The incident happened at around 12.25pm on Wednesday, November 19.
Police have confirmed the officer was on duty and on the way to an emergency at the time of the crash.
No other vehicle is believed to have been involved.
The officer died at the scene.
The A12 was closed for a significant period while specialist officers carried out investigation work.
Authorities have not yet released further details.
Chief Constable Ben-Julian Harrington said: “My thoughts and prayers, and those of the entire Essex Police family, are with the officer’s family and friends.
“I want to pay tribute to our professional and courageous colleague. He was a dedicated professional who died doing his job – protecting and serving the people of Essex. I will always be grateful for his service.
“We are supporting the officer’s colleagues and his family at this extremely difficult time.
“I would ask that people do not speculate about the collision and the circumstances around it.
“Please let our experienced and professional investigators carry out their work.
“I also want to thank the public who were affected by the collision for their patience, understanding, and co-operation with officers and our emergency service colleagues who responded to the collision.”
A spokesperson for Essex Police said: “Sadly, we can confirm a police officer died in the line of duty yesterday (Wednesday 19 November) following a collision on the A12.
“The officer was responding to an emergency at the time of the collision which took place on the stretch of road near Ingatestone at around 12.25pm.
“At this stage we do not believe any other vehicle was involved and, sadly, the officer died at the scene.
“The road was closed for a significant amount of time while specialist officers responded and investigated at the scene.”
