[7] In 1964, Koso nominated Muivah for the general secretary of Naga National Council at Tuzol Sokha, a forested area near Viswema village.
[8] Koso was elected a member of the first Nagaland Assembly in February 1964 from the Southern Angami II Assembly constituency constituency as a Naga National Democratic Party candidate (later became the Nagaland People's Council) and later became the leader of the Opposition[4] till it resigned en bloc after a ceasefire agreement was signed in September 1964.
[7] In 1966, Koso was part of the five member-Nagaland Peace Commission formed in Kohima as an initiative of the Nagaland Baptist Church Council.
[10] He was re-elected in 1974 from the Southern Angami II constituency, and was unanimously chosen as the leader of United Democratic Front party and was appointed the Chief Minister of Nagaland.
[7] Koso was the founding member of the Nagaland State Branch of the Indian Red Cross Society in 1982, and served as its Chairman till he resigned in 2004, on health grounds.
[4] Koso died on 3 March 2008 at 07:10 Indian Standard Time (UTC+05:30), at his personal residence in Daklane Ward, Kohima after a prolonged illness and his remains were laid to rest at Viswema.