The current prevailing take-make-waste economy has caused the global climate crisis, operating outside the Planetary Boundaries of our planet (Rockström et al., 2009), disrupting nature's balance and affecting all life on earth (WWF and Global Footprint Network, 2019). Both the European Commission and the European Environmental Agency (EEA) sees the transition to a circular economy (CE) within the product category: textiles, apparel and fabrics as a priority to address the climate impact of the textile and clothing industry (Manshoven et al., 2019). Even though there is much research done on how design and products can help companies transition to a CE, there is still an unexplored dimension of the role that consumers play in this transition. Thus, this master thesis aims to fill this research gap by exploring consumer behaviour in different consumption phases as well as the role of consumers in the circular textiles economy and investigate how sustainable clothing companies can design to engage consumers in a circular behaviour and role. By doing so, it is hoped to contribute to a better understanding of the dimension of the consumer in the circular textiles economy and to identify ways to fulfill the CE principle - keep products and materials in use. The study was conducted through a novel implementation of Research through Design in combination with Interactive Research by using the Design Thinking framework as a research process. The research was executed in close collaboration with the Swedish outdoor clothing company Houdini Sportswear.  The results show that a number of Circular Consumer Behaviours are desired to be acted out in four identified phases of a Circular Clothing Consumption Process: Lifestyle Creation, Product Acquisition, Product Use and Product Dispossession. Furthermore, it was found that the role of the Circular Consumer is very complex and consists of various sub-roles on four layers: Functional, Emotional, Life Changing and Social Impact. On the basis of this knowledge, the theoretical concept of Design for Circular Consumers was developed. On the basis of this theory, the Design for Circular Consumers Tool was created as the key contribution of this thesis. This tool facilitates the design of experiences that engage consumers in the circular textiles system and subsequently support clothing companies in their transition to circular business models as a way to address the climate impact of the textiles industry.