The origins of Trongsa Dzong lie in the vision of the goddess Pelden Lhamo. She appeared to Ngagi Wangchuk (1517-1554) who set out from Tibet on a pilgrimage to Bhutan. One night in 1543 he saw a blue flame hovering above a spur of rock in the forest. Drawn by this light, Ngagi Wangchuk ventured down into valley where the powerful Palden Lhamo told him that this was a sacred place destined to become an important religious center. With the temple he built there he laid the foundation of what was to be become Trongsa Dzong.
At the beginning of the 17th century the territory of present- day Bhutan consisted of the various small principalities. The establishment of unified state was only achieved by Zhabdrung Ngawang Namgyal(1594-1651) who united the independent principalities into one theocratic state. In years of war and constant danger , the Zhabdrung established a seat of power IN Trongsa which give its strategic location between east and west would play a crucial role as the base camp for military campaign .
The Zhabdrung’s policy was to entrust the task of expanding his domain to the east to men who had his absolute confidence. Thus in 1643 he gave his close confidant Choegyal Mingyur Tenpa the order to expand the Dzong and appointed him as first Ponlop of Trongsa .He succeeded in conquering central and eastern Bhutan by the end of 1655 four year after Zhabdrung had pass away.