In the early '80s, he was among the many Isaaq military officials who defected from the SNA due to the widespread nepotism and corruption of the Barre regime.

Kosar joined the newly formed Somali National Movement and was the leader of its Military wing where he trained and led SNM fighters on many operations against the SNA.

This power struggle within the SNM led to the convening of an emergency meeting of the central committee in November 1983 which took place in Harar, Ethiopia.

Kosar was able to secure 2 thirds of the votes and was declared chairman, soon after the religious civilians were effectively purged from leadership roles and the movement took on a more militaristic face.

Under Kosar's leadership, the SNM expanded its relations with the Derg beyond military and security matters into politics which led to a meeting at Dire Dawa between him and Mengistu in 1984.