A walker along Thorpeness beach came across the dolphin-like animal with a significant injury near its head.
He estimated the porpoise was around five feet long.
This article contains an image that some readers may find distressing.
The discovery comes as many other animals have been found along the county’s coastline in the last week.
Another porpoise was found in Felixstowe on Monday and on the same day, two further dolphins washed up in Pakefield.
The porpoise found this week is likely to be a harbour porpoise due to its small size and blunt head.
READ MORE: Drone footage shows devastating erosion impact in Thorpeness
The porpoise shows signs of injury (Image: Submitted)
Although porpoises look like dolphins, they are more closely related to belugas and narwhals.
If you find a deceased animal on a beach, it should be reported to the Cetacean Strandings Investigation Programme on 0800 652 0333.
You should give a description of the location and date found, overall length, condition of the animal, as well as your contact details, should further information be needed.