Aminul Karim was commissioned in Bangladesh Army as an officer in 1975 in the Regiment of Artillery. He commanded two field units and two field brigades including one independent brigade. He commanded a unit in the Chittagong Hill Tracts in counterinsurgency role. He worked as a brigade major in an independent brigade and a staff officer in the military operations directorate at Army Headquarters. He also worked at the Military Secretary's Branch at Army Headquarters. Aminul was a faculty member of Defence Services Command and Staff College from 1992 to 1995. From 2001 to 2002, he served as a faculty member at the
National Defence College, training senior military and civilian officials in defence and senior management of national security. From 2002 to 2003, he served as the Quartermaster General of the
Bangladesh Army. He served as the Adjutant General of the Bangladesh Army in 2004. From 2004 to 2005 he served as the General Officer Commanding of an Army Division of the Bangladesh Army. Regarding the transfer of power, he stated:“The main architect of One-Eleven was Army Chief Moeen U Ahmed. He wanted to impose martial law. However, the U.S. Embassy in Dhaka intervened, meeting with Major General Jahangir Alam Chowdhury, the then-PSO of the Armed Forces Division, and discouraged him from doing so. Lieutenant General Masud Ahmed informed me about this. Jahangir Alam Chowdhury and Moeen U Ahmed were coursemates and shared a close relationship. On January 11, 2007, at approximately 1:30 pm, Moeen U Ahmed, the three service chiefs, PSO
Major General Jahangir Alam Chowdhury, and acting DG of DGFI Brigadier General Fazlul Bari went to Bangabhaban. At that time, Moeen U Ahmed showed the President a letter from the United Nations, although that letter was later proven to be fake. After about two hours, they left with President Iajuddin Ahmed’s signature."Furthermore, he stated that he had been offered an ambassadorship, which he declined as he wanted to stay close to his sick mother. He was later sent on forced retirement from
Bangladesh Army on March 12, 2009. == Academic career ==