The city was founded in the late 18th century by Thao Kham Phong, descendant of Phra Wo and Phra Ta, who escaped from King Siribunsan of Vientiane into Siam Kingdom during the reign of King Taksin the Great. Later Thao Kham Phong was appointed to be “Phra Pathum Wongsa” and the first ruler of Ubon Ratchathani. In 1792 Ubon Ratchathani became a province. it was also the administrative center of the monthon Isan. Until 1972 the Ubon Ratchathani province was the largest province of Thailand in area. Yasothon province was split off in 1972 and followed by Amnat Charoen province in 1993. Ubon now ranks 5th in area.
Ubon Ratchathani sits on the northern bank of the Mun River. The south bank of the river is occupied by the suburb of Warin Chamrap (Warin for short), which is effectively incorporated into the city.
The city was attacked by French forces in 1940 in retaliation for Thai attacks on French Indonchinese towns.
Ubon grew extensively during World War II when Japanese forces brought in prisoners of war by rail from Kanachanaburi. One legacy of this is a monument in the city's central Thung Si Meuang Park erected by British POWs in gratitude to the citizens of Ubon for assisting them. During the Vietnam war, United States armed forces constructed the in-town Ubon Royal Thai Air Force Base, which is now also a dual-use commercial airport.
Lao influence is evident in the architectural structure of some of the city’s religious buildings.
The city has branches of the National Archives of Thailand and National Museum of
