Undersecretary for Budget Operations, Department of Budget and Management (1986–1991)

Diokno served as undersecretary for Budget Operations of the Department of Budget and Management from 1986 to 1991 under President Corazon Aquino.^[11] In this capacity, he provided technical assistance to several major reforms such as the design of the 1986 Tax Reform Program,^[12] which simplified income tax and introduced the value-added tax (VAT), and the 1991 Local Government Code of the Philippines.^[13]

Secretary of Budget and Management (1998–2001)

During the Estrada administration, Diokno initiated and instituted several reforms that would enhance transparency and improve the efficiency of the delivery of government services. The first major reform instituted was the "what you see is what you get" or WYSWIG policy that is a simplified system of fund release for the General Appropriations Act (GAA). This allowed agency heads to immediately plan and contract out projects by just looking at the GAA, which is available in print and at the DBM website, without waiting for the issuance of an allotment authority.^[14] Diokno initiated the reform of the government procurement system (GPS) through the adoption of rapidly improving information and communications technology. He secured technical assistance from the Canadian International Development Agency (CIDA) to help the GPS develop an electronic procurement system along the lines of the Canadian model. By August 1999, the DBM had two documents necessary to initiate reforms in public procurement. In early 2000, Diokno and USAID successfully concluded a substantial technical assistance program for the DBM's budget reform programs, which now included procurement reform.^[15] Other budget reforms instituted by Diokno concerned procedures for payment of accounts payable and terminal leave/ retirement gratuity benefits. The release of cash allocation were programmed and uploaded to the department's website while payments were made direct to the bank accounts of specific contractor.^[14]

Secretary of Budget and Management (2016–2019)

In his third tour of duty as Budget Secretary, Diokno intended to pursue an expansionary fiscal policy to finance investments in human capital development and public infrastructure. In addition, he seeks for the passage of a Budget Reform Bill to ensure the compliance of future budgets with the pertinent laws of the land. He also aims to re-organize and professionalize the bureaucracy with a Government Rightsizing Act.

Governor of the Bangko Sentral ng Pilipinas (2019–2022)

On March 4, 2019, President Duterte appointed Diokno as the fifth Governor of the Bangko Sentral ng Pilipinas (BSP), of which he will finish the unexpired term of his late predecessor, Nestor Espenilla Jr. which was supposed to end in July 2023.^[16]

Secretary of Finance (2022–2024)

On May 26, 2022, then President-elect Bongbong Marcos announced that he would nominate Diokno as the next Finance Secretary in his incoming administration,^[17] replacing Diokno in the role of the governor of BSP, with Felipe Medalla, who will finish Diokno's unexpired term.^[18] Diokno subsequently took his oath at the Malacañang Palace on June 30, 2022, following the inauguration of the former as president.

On January 12, 2024, Diokno was succeeded by Batangas Representative and Deputy Speaker Ralph Recto as the Finance Secretary, after the latter was appointed by President Marcos on January 11, with Recto taking the oath of office the next day.^[19][3]

Monetary Board Member of the Bangko Sentral ng Pilipinas (2024–present)

On January 12, 2024, President Marcos subsequently appointed Diokno as one of the six members of the Monetary Board of the Bangko Sentral ng Pilipinas, replacing Peter B. Favila in the position.^[3]