A veterinary team tried "to help stabilize its illness but finally, the whale died" on Friday afternoon, the post said.
Thailand's Department of Marine and Coastal Resources found the whale last week in the south of the country, near the Malaysian border, unable to swim.
Thailand's Marine and Coastal Resources Department has released graphic images from the post mortem to highlight the need to reduce plastic pollution, especially in the countdown to World Oceans Day on June 8.
"If you have 80 plastic bags in your stomach, you die", he told AFP. Pilot whales primarily eat squid but are also known to hunt octopus, cuttlefish and small fish when squid prove elusive, the American Cetacean Society said.
From street vendors selling satay to shop clerks putting purchases into multiple bags, Thais use a huge amount of plastic.
A whale has died in southern Thailand after swallowing more than 80 plastic bags, an official said.
Across the world, we dump about eight million tons of plastic into the ocean every single year, according to the United Nations Environment Programme. Kenya a year ago enacted the world's toughest law against plastic bags.
The dead whale is likely to have been the short-finned species of pilot whale, which have been nicked named the "cheetahs of the sea" due to their high-speed pursuits of squid.