He then continued his higher education at the Faculty of Economics of the University of Indonesia (UI), specializing in the field of demography.

While still a student, he, together with Canadian demographer Nathan Keyfiz, wrote a book entitled "The Problem of Indonesian Population and Development."

The foreword was written by former Vice President Mohammad Hatta, who wrote, "An Indonesian son with his knowledge of the problems of his homeland, has been able to work with Canadian statisticians.

Although he did not become president for the next two years, Suharto began to build the foundations of the government that would later be referred to as the New Order regime.

[10] In 1971, Widjojo was appointed State Minister for National Development Planning, a position he held until the early 1980s.

[11] As minister, he and his colleagues in the 'Berkeley mafia' used a neo-Keynesian approach to balance the state budget, control the money supply, re-establish the position of financial institutions, and open the door as wide as possible for foreign investors.

Economist Mudrajad Kuncoro, who is a professor of Economics at Gadjah Mada University, in his column in the Gatra magazine, said that the focus of the Five-Year Development Plan was macroeconomics.

With this flow, regional development is more prominent because both planning and implementation are “centralized.”[4] During his career in government, Widjojo was the head of many Indonesian delegations to numerous international meetings such as the Inter-Governmental Group on Indonesia (IGGI), the Paris Club, and World Bank and International Monetary Fund (IMF) meetings.

However, during the Abdurrahman Wahid administration, he was trusted to lead the Indonesian Economic Team at the Paris Club meeting in mid-April 2000 to discuss rescheduling the repayment of Indonesia's debt for the period April 2000 – March 2002 amounting to US$ 5.9 billion.

In 2010 a collection of some of his main reports and speeches during his period as an adviser was published as Pengalaman Pembangunan Indonesia (The Indonesian Development Experience).

His role as a major policy-maker in Indonesia was recognised at an official ceremony in the Planning Bureau (Bappenas) following the service.

After lying in state for a few hours in Bappenas to provide an opportunity for mourners, including President Susilo Bambang Yudhoyono, to pay their respects, Widjojo was buried at Kalibata Heroes' Cemetery in South Jakarta at a ceremony led by Vice President Boediono.

In October 2012, Widjojo was recognised as the "father of Indonesian demography" during a seminar at the 62nd anniversary of the Economics Faculty, University of Indonesia.