Many cities of the world are faced with multiple sustainability challenges, for example related to food and energy supply, transportation, waste management, clean air, and more. Preferably, these challenges are addressed with broad and interconnected solutions with the ambition of addressing several challenges simultaneously, in this paper referred to as multi-functional urban solutions. Implementation of multi-functional urban solutions requires well informed decisions, supported by knowledge about the potential contributions that the solutions can make to a more sustainable city as well as on issues that may hinder or facilitate their implementation. Thus, in this paper, we suggest a soft multi-criteria decision analysis method that can be used to gather and structure this knowledge. This method acknowledges the importance of incorporating local knowledge, is based on life-cycle thinking, and is flexible and open-ended by design so that it can be tailored to specific needs and conditions. The method contributes to existing practices in sustainability assessment and feasibility studies, linking and integrating potential and performance assessment with issues affecting solutions’ feasibility of implementation. This method offers a way for local authorities, researchers and exporting companies to organize and structure the diverse range of knowledge to be considered for more informed decisions regarding the implementation of multi-functional urban solutions. While the main contributions of the paper are methodological, brief descriptions of two studies that have applied this method to assess biogas solutions are shown as clarifying examples. One of these studies was performed in Chisinau, Moldova and the other in Johannesburg, South Africa.