On 19 September 1988, he was officially commissioned into the Royal Brunei Land Forces as a lieutenant. Aminuddin took up many positions during his military career such as a platoon leader of Company 'D' 1st Battalion (1Bn RBLF), troop leader of the Auxiliary Battalion, commanding officer in the Infantry Battalion, deputy commanding officer and commanding officer of the 2nd Battalion (2Bn RBLF), Commander of the RBAF Training Institute and the Commander of the RBLF. On 31 December 2009, he was appointed as the 8th Commander of the RBAF by succeeding Major General Halbi bin Mohammad Yussof. Aminuddin would then be succeeded by Mohammad Tawih on 29 January 2014.
