[1][2][3] Mammen was born into the Kandathil family on 31 July 1921 as the sixth child of K C Eapen who was the Managing Director/Deputy Chairman of Travancore National Bank Ltd and Kunjandamma, in Thiruvananthapuram.
[4][5] His father K C Eapen later became the manager at the National Quilon Bank, and they lived opposite the Kerala Government Secretariat where freedom fighters used to converge to make speeches.
Mr Mammen and his cousin C. G. Philip were the partners of Ithikkara tile factory at Ithikkara, Kollam district, his brother K E Cherian started Bank of New India [5] He became the president of the Travancore Students Federation while he was an intermediate student at College of Fine Arts Trivandrum.
During this period, he was jailed for urging students to join the freedom struggle, during a public meeting held at Thirunakkara.
He was the candidate for the newly formed Praja Socialist Party in the 1952 Travancore-Cochin Legislative Assembly election and ended up coming second by 500 votes.