Officers were called to the scene, inside a disused building at Billion Plaza in Moo 1, Kathu, at around 5:40pm.
Also arriving at the scene were a forensic doctor from Vachira Phuket Hospital and rescue workers from the Kusoldharm Phuket Foundation.
The deceased was identified as a Thai male, approximately 40 years old, with a distinctive Hanuman tattoo on his back.
No identification documents were found on the body, which is believed to have been there for about seven days. Police found no signs of a struggle or foul play at the scene.
Local residents told police the man was believed to be a homeless individual with possible mental health issues who had been living in the abandoned building for about two months.
Preliminary investigations suggest the man may have died from a chronic illness. His body was taken to Vachira Phuket Hospital for medical examination to determine the exact cause of death.