After graduating with an undergraduate degree (S1 in the Indonesian system) at the University of Indonesia in 1958, Sumarlin served as a teaching assistant for some years.

During one of the meetings at the National Palace, Cabinet Secretary Sudharmono is said to have casually gestured towards Sumarlin asking, "Who is the boy sitting there, Widjojo?"

While serving as Deputy Chair of Bappenas, Sumarlin was closely involved in drafting government reforms with guidance from Cabinet Secretary Sudharmono.

He was regularly involved, for example, in the preparation of the key Annex document attached to the Presidential State Address released on August 16 each year for presentation to parliament.

Although of modest stature and known for a disarming smile, Sumarlin became an effective minister during the period of the New Order government in Indonesia.

Previously he had held the post of deputy minister for Fiscal and Monetary Affairs in the Indonesian National Planning Agency.

Subsequently, before the fall of the New Order government in 1998, he was appointed to the senior post of Chairman of the Supreme Audit Agency (Badan Permeriksaan Keuangan, or BPK).