He was actively involved as a peacemaker between Ethiopia and Eritrea working on an interfaith committee chaired by Abune Paulos, the Patriarch of the Tewahedo Church.

Mammo was left orphaned during the Second Italo-Ethiopian War when the air force of Fascist Italy bombed his tiny village, Bashagia in what was then Wollo Province.

[2] His writing skill has enabled him to secure journalistic jobs at the United States Information Service, a section of the American Embassy, and the Russian Cultural Center at Addis Ababa.

He also served at the Ethiopian Ministry of Information where he met and befriended authors like Berhanu Zerihun and Mengistu Gedamu.

Shortly after the outbreak of the Ethiopian Revolution in 1974, Mammo became an editorial staffer of the magazine Yekatit.