He started his reign on 1578 after deposing his brother Sadashiva Malla.

He annexed Patan in around 1600 which was then ruled by the descendants of Vishnusimha since the time of disintegration after Yakshya Malla.

Harihara Simha died shortly afterwards, and his eldest son Siddhi Narasimha Malla was the governor of Patan.

[2][3] After the death of Shivasimha in 1619, Lakshmi Narasimha Malla, another son of Harihara Simha, succeeded him as the King of Kantipur, and Siddhi Narasimha Malla declared Patan independent from Kantipur.

[4] Thus, the kingdoms of Kantipur and Patan united by Shivasimha were divided again by his grandsons.