Historically, the area was Mueang Wiang Kaen, on the Ngao River. It was founded about the same time of Sukhothai Kingdom and Chiang Rai.
The government separated the three tambons Muang Yai, Po, and Lai Ngao from Chiang Khong district to create a minor district (king amphoe) on 1 April 1987.[1] It was upgraded to a full district on 7 September 1995.[2]
The district is divided into four sub-districts (tambons), which are further subdivided into 41 villages (mubans). There are no municipal (thesabans), and four tambon administrative organizations (TAO).