There is a legendary story associated with the history of Purnagiri Temple. According to the legend, in the year 1632, a trader named Chandra Tiwari from Gujarat sought refuge with King Gyan Chand of Champawat. Mata Punyagiri appeared in his dream and expressed her desire for a temple to be built. Subsequently, the construction of Purnagiri Temple began. Since then, this temple has been a place of worship and attracts a large number of devotees. As per Hindu mythology, during the Satya Yuga, Goddess Sati, the daughter of Daksha Prajapati, defied her father's wishes and married Lord Shiva. In retaliation, Daksha Prajapati performed a grand Yagna and invited all the deities except Lord Shiva. Sati, despite not being invited, expressed her desire to attend the Yagna. Lord Shiva tried to dissuade her, but she insisted. When they reached the Yagna, Daksha insulted Lord Shiva, which Sati found unbearable. In her grief, she self-immolated. Upon seeing Sati's burning body, Lord Shiva became furious, and in his rage, he destroyed Daksha's Yagna. He then carried Sati's charred corpse on his shoulder, and his Tandava dance caused havoc in the universe. To stop this destruction, Lord Vishnu intervened and dismembered Sati's body using his Sudarshana Chakra. The places where her body parts fell are revered as Shakti Peeths, with Purnagiri being the location where her navel is believed to have fallen.

Purnagiri Temple holds great significance among all the famous temples in Uttarakhand. Devotees visit this temple throughout the year, with a large influx during the Chaitra Navratri. Many believe that visiting Siddh Baba Temple after worshipping Goddess Purnagiri is essential for the success of their journey. It is also believed that if a child's Mundan is performed at this temple, the child will have a long and intelligent life.

The architectural style of Purnagiri Temple is a blend of North Indian and Nepali styles. Within the temple complex, there are several smaller temples dedicated to various deities, with the main temple dedicated to Goddess Purnagiri. The temple is made of stone and features intricate carvings on its walls and pillars. The idol of the Goddess is carved from black stone and adorned with gold ornaments and colourful clothes. There is also a large hall in the temple where devotees can sit and perform worship.

Devotees offer fruits, chickpeas, citrus fruits, dried fruits, flowers, and sarees to Goddess Mata in Purnagiri Temple.