The Pratap Malla inscription of Kathmandu details that Gangadeva came to the throne in 1147 and was considered to be a very brave King.
He was a contemporary of King Madanpala of the Pala's of neighbouring Bengal and led attacks against them regaining some of the territories that had been lost during his father Nanyadeva's reign while also gaining new territory.
The Ramacharitam also details that both Nanyadeva and Gangadeva claimed some sort of political authority in Gauda as he was declared as Gaudadwhaj.
[1][2] Gangadeva was notable for his administrative reforms and added Darbhanga as an additional capital of the Karnat dynasty along with Simraungadh.
The village of Gangapur Rajni in Madhepura district of Bihar was named after Gangadeva.