[3][4] Trat is believed to derive from Krat (กราด), the Thai name for the tree Dipterocarpus intricatus, common to the region and used to make brooms.

[citation needed] Under King Chulalongkorn (Rama V), Trat and Chanthaburi province were briefly occupied by the French.

In a complicated exchange of territory, Trat (and Chanthaburi) was returned on March 23, 1906, but Thailand relinquished the area around Siem Reap and Sisophon in present-day Cambodia.

When the Vietnamese pushed the Khmer Rouge out of Cambodia in 1985, Pol Pot fled to Thailand and made his headquarters in a plantation villa near Trat.

The area around Trat is rich in gemstone mines, whose yield (rubies and sapphires) is processed right in the town.