Brigadier General Aldi bin Haji Hassan was commissioned as a 2nd Lieutenant in October 1998 after completing his Officer Cadet Training at the SAFTI Military Institute (SAFTI MI), Republic of Singapore, in October 1997. He began his military career as the Platoon Commander of ‘A’ Company, First Battalion Royal Brunei Land Forces.

Over the course of his military service, Brigadier General Aldi has held various key command and staff appointments. These include Officer Commanding of the Special Task Platoon 1Bn RBLF, Staff Officer Grade 3 Training at RBLF Headquarters, Second-in-Command of Courses Company at the Training Centre RBAF, Officer Commanding of the Officer Cadet School RBAF, and Officer Commanding of C Company 1Bn RBLF. He was later appointed Officer Commanding of the School of Infantry at the Training Institute RBAF and subsequently served as the Acting Chief Instructor of the same institute. His leadership capability continued to be recognised when he was appointed as the Commanding Officer of 1Bn RBLF, followed by a staff appointment as Assistant Chief of Staff Admin at RBLF. He then served as Deputy Commandant of the Training Institute RBAF, Chief of Staff of the Royal Brunei Land Forces, and later, Chief of Staff at Joint Force Headquarters RBAF. In September 2024, Brigadier General Aldi was appointed as Deputy Joint Force Commander and subsequently served as the Acting Joint Force Commander starting 11 January 2025 until 31 July 2025. On 1 August 2025, he officially assumed the appointment as the 15th Commander of the Royal Brunei Land Forces