Mamun was serving as Director General of the Rapid Action Battalion (RAB), the elite force of Bangladesh Police-- since April 2020.

Mamun joined Bangladesh Police Service as Assistant Superintendent of Police in February 1989. He has served in various capacities of Bangladesh Police where he proved his professionalism, dedication, and excellence.

He has served as Assistant Superintendent of Police, Additional Superintendent of Police in various districts, Superintendent of Police in Nilphamari district, Deputy Police Commissioner in Dhaka Metropolitan Police (DMP), Assistant Inspector General (AIG) (Establishment) of Police Headquarters, and AIG (confidential) of Police Headquarters, Additional Deputy Inspector General (Addl DIG) of Dhaka Range Police, Deputy Inspector General (Admin & Op) of Police Headquarters, DIG Mymensingh Range and Dhaka Range Police.

Mamun also served as Additional IGP (HRM) of Police Headquarters and Chief of Criminal Investigation Department (CID) of Police.

Born in Sunamganj in 1964, Chowdhury Abdullah Al-Mamun completed his graduation and post-graduation in Sociology from the University of Chittagong.

He achieved Bangladesh Police Medal (BPM) and President Police Medal (PPM) for his outstanding performance in police service.

Mamun has made outstanding contributions to UN peacekeeping missions in Bosnia-Herzegovina, Liberia, and Darfur. He participated in several prestigious professional pieces of training at home and abroad.