Managing project sustainability is becoming important in the last two decades since the Earth Summit in 1992. An increasing number of projects have built in sustainability considerations into project design and implementation. Recent research findings show that lack of sustainability knowledge for project managers is a key barrier to drive projects and programs contributing towards a sustainable society. Definitions and approaches (pillar-based and principles-based) to sustainability in project management together with project manager competence requirements are discussed. The purpose of this chapter is to devise an assessment tool for project managers incorporating the concept of pillar-based and principles-based sustainability approaches as well as the EIA-driven and objectives-led assessment methodologies. Criteria for selecting assessment scheme appropriate to various project initiatives are developed. Integrating selected assessment methodology into sustainability evaluation framework within the project life cycle forms a complete tool. This chapter contributes to devising a practical assessment tool for project managers in managing project sustainability.