During 1196, Nicholas was one of the leaders of the Bagler party together with the nobleman Reidar the Messenger from Viken and Sigurd Jarlsson, a bastard son of Erling Skakke. Archbishop Erik Ivarsson also gave his support. The Bagler chose Inge Magnusson, who was claimed to be the illegitimate son of King Magnus V, as their candidate for king. The Baglers established themselves in the Viken area, which was both Nicholas' bishopric and King Magnus' old power base. On 18 June 1199 the two fleets met at the naval Battle of Strindafjord. Here Sverre won a crushing victory and the surviving Baglers fled.