Department director-general Phanombut Chantarachot said the archaeological wonder was among the World Heritage Committee's 53 discussions in Riyadh, Saudi Arabia from September 10 to 25.
He expects the committee to announce the listing on Tuesday.
If the ancient town were to be listed as a World Heritage Site, it would be Thailand's fourth in the cultural category, he said.
This archaeological wonder was proposed to Unesco in 2019. Evidence shows it was founded about 1,700 years ago.
The remnants of the city are located on 4.7 square kilometres of land in Si Thep district, about 200 kilometres northeast of Bangkok.
It was home to a late prehistoric community before becoming an important town in the Dvaravati or Mon Kingdom era (1,400-1,000 years ago). It then flourished for the next 200 years during the Khmer Empire before being abandoned.
The archaeological site is divided into outer and inner cities, comprising a maze of ancient walls, moats and pagodas.
Highlights include:
▪︎ Prang Si Thep – a Khmer-style religious tower
▪︎ Prang Song Phi Nong – a Khmer tower made of laterite
▪︎ Prang Ruesi – another tower dating back to the same Angkorian period
▪︎ Khao Klang Nai Archaeological Site – the mountain-like structure is thought to have stored weapons and valuable items
▪︎ Khao Klang Nok Archaeological Site – another mountain-shaped stupa, dubbed "Thailand's Pyramid"
▪︎ Khao Thamorat Cave – a limestone cave adorned with bas-relief sculptures
Apart from historical sites, the archaeological ruins have also revealed human and animal remains, as well as prehistoric artifacts.
Thailand already has three World Heritage sites in the cultural category. They are:
▪︎ Ban Chiang Archaeological Site (1992)
▪︎ Historic City of Ayutthaya (1991)
▪︎ Historic Town of Sukhothai and Associated Historic Towns (1991)
Several more sites are currently being considered for Unesco listing. They include:
▪︎ Ensemble of Phanom Rung, Muang Tam and Plai Bat sanctuaries, Buri Ram province
▪︎ Phra That Phanom, its related historic buildings and associated landscape, Nakhon Phanom province
▪︎ Monuments, sites and cultural landscape of Chiang Mai, capital of Lanna
▪︎ Wat Phra Mahathat Woramahawihan, Nakhon Si Thammarat province
▪︎ Phuphrabat Historical Park, Udon Thani province