Until 2007 Harnai had been a tehsil of Sibi District, in August the Balochistan Government announced Harnai district would be created by splitting Sibi district and forming the new district from Harnai and Shahrag tehsils and the sub-tehsil of Khost. the population of Harnai is predominantly Pashtun followed by Baloch.
Harnai is surrounded by mountainous ranges. The minimum and maximum winter temperature of the area is -2˚C to 20˚C. The summer is extreme in the area and the minimum and maximum temperature falls between 20˚C to 48˚C. Harnai has a fertile rainy season during monsoon time. In general Harnai has a pleasant weather in winter season. Harnai is one of the most beautiful cities of the Balochistan Province with the plenty of water available in the streams. It is the only area of the production of the fresh vegetables and fruits with fresh and clean water in the whole Balochistan.