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"[clarification needed] and the first ruler of Ubon Ratchathani. In 1792 Ubon Ratchathani became a province, and was also the administrative center of the monthon Isan. Until 1972 Ubon Ratchathani was the largest province of Thailand by area. Yasothon Province was split off from Ubon Ratchathani Province in 1972, followed by Amnat Charoen Province in 1993. Ubon Ratchathani Province now ranks fifth in area.
Ubon Ratchathani sits on the north 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 Indochinese towns.
Ubon grew extensively during World War II when Japanese forces brought in prisoners of war by rail from Kanchanaburi. One legacy of this is a monument in the city's central Thung Si Meuang Park erected by British prisoners of war 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 Thailand.