The understanding of the role of the contracting authority in public procurement is important to understand the underused potential of public procurement to contribute to the sustainable development of society. In particular, the concept of public-private cooperation was suggested to increase this potential, but not enough is known about how the interaction has to take place in order to address the behavioural factors that cause the barriers to sustainable public procurement. The results of this research showed that the leading role of the contracting authority could facilitate sustainable procurement by increasing engagement, interaction and collaboration. A strategic planning approach to support the public-private cooperation in the procurement process is needed. Based on the Framework for Strategic Sustainable Development, a support for the contracting authority was designed to guide the strategic planning of the procurement process. The suggested design of Support for Strategic Sustainable Procurement was evaluated and found likely to support the contracting authority in strategically leading the public procurement process to leverage the potential of public procurement on the transition towards a sustainable society.