Based and as declared policy of the state (Republic of the Philippines) that the territorial and political subdivisions of the State shall enjoy genuine and meaningful local autonomy, wherein a system of decentralization be instituted (Rule I, Article III, Republic Act No. 7160, Rules and Regulations Implementing the Local Government Code of 1991), and,
Upon the organization of the Autonomous Region under Republic Act No. 6734, an act providing for the Organic Act for the Autonomous Region in Muslim Mindanao (Section 4, Par. 1 Article XIX – Transitory Provisions) the line agencies and offices of the National Government dealing with local government, social services, science and technology, labor, natural resources and tourism including their personnel, equipment, properties and budgets, shall immediately placed under the control and supervision of the Regional government.
The President, Republic of the Philippines, Her Excellency, President Corazon C. Aquino on October 12, 1990 issued Executive Order 425: Placing under the control and supervision of the Autonomous Regional Government, the line agencies and offices of the National Government within the Autonomous Region in Muslim Mindanao dealing with Local Government, Social Welfare, and Development, Science and Technology, Labor and Employment, Environment and Natural Resources and Tourism, (Section 4, Executive Order No. 425).
Thus, the legal basis in the creation and existence of DILG-ARMM.