The first inventory of the ruins was done in 1901 by the French geographer Etienne Aymonier. They were put under governmental protection by announcement in the Government Gazette, Volume 53, section 34, from September 27, 1936. Most of the restorations were done from 1964 to 1969 as a joint Thai-French project. The historical park, now managed by the Fine Arts Department, was officially opened by Princess Maha Chakri Sirindhorn on April 12, 1989.
In the aftermath of the fall of the Ayutthaya Kingdom in 1767, attempts were made to set up five separate states, with Prince Teppipit, a son of king Boromakot, attempting to establish Phimai as one, holding sway over eastern provinces including Nakhon Ratchasima. The weakest of the five, Prince Teppipit was the first defeated and was executed in 1768. Phimai had also been an important town at the time of the Khmer. The temple Prasat Hin Phimai, located in the center of the town, was one of the major Khmer temples in ancient Thailand, connected with Angkor by an ancient Khmer Highway, and oriented so as to face Angkor as its cardinal direction. The site is now protected as the Phimai historical park.
Phimai has recently been the base of operations for the excavation of Ban Non Wat.