One of the ways that Transmission System Operators (TSOs) can become more sustainable is by integrating sustainable goals in their projects using the associated procurement and tender processes. However, there are several limitations related to this integration. This research aims to identify these challenges by looking at the Dutch TSO, TenneT and its specific context. Furthermore, the research aims to provide a decision-support framework through which these limitations can be countered and the integration of sustainable goals in projects can be achieved. First, a literature study was conducted to define sustainability and the concepts associated with it. To properly understand the context of TenneT and identify the limitations associated with sustainability, company professionals were interviewed. This pointed to the need for prioritisation and gradual integration of sustainability measures. A desktop study was also conducted to identify the company’s sustainable goals, their associated measures, and their real-life applications. A decision-support framework for integrating sustainable goals in projects, based on Multi-Criteria Decision-Analysis (MCDA) was proposed. Using the Best-Worst Method (BWM), as the selected MCDA method, developed by Rezaei (2015), a sustainability workshop was organised where decision-makers from TenneT were asked to select relevant sustainability goals for TenneT, and the ones selected by three or more decision-makers were then used for performing the BWM. To avoid focusing on already well-performing sustainability goals, the performance of their associated measures was studied, using a Maturity Model based on the work of Silvius and Schipper (2015). Finally, an Importance-Performance Analysis (Martilla and James 1977) was performed, to assess future actions for each sustainable goal. The BWM showed that the Planet aspect was selected as the most important one for stimulating sustainability in projects. Additionally, Reducing Emissions was selected as the most important sub-aspect while in the People aspect, Health and Safety ranked first. The Maturity Model showed that the least integrated goals in projects are Human Rights, Labour Conditions and Decent Work, Energy Consumption, Materials and Natural Resources and Circularity and Waste. The BWM and Maturity Model also produced interesting results regarding the awareness of decision-makers and how they perceive sustainable goals and the performance of their associated measures in projects. Based on the Importance-Performance analysis, the research suggests integrating the sustainable goal of Circularity and Waste in the company’s following projects. This can be achieved by using existing sustainable measures, such as the Raw Material Passport (RMP), in the tender process. Using measures such as the RMP in the pre-qualification phases or selection phase, as entry requirements with specific targets to be met, or as an award criterion, aiming to create added value for the project, can stimulate the contractors and suppliers to act more sustainably. This will in turn increase TenneT’s sustainable performance and will help the company meet its own sustainable targets.