This research investigates how professional designers engage with sustainability in their practices, focusing on the early ideation phase. A comprehensive literature review identified gaps in existing tools and methods, highlighting a lack of practical guidance for addressing sustainability within organisational and societal contexts. Semi-structured interviews with design practitioners provided insights into the challenges designers face, including conflicting stakeholder priorities, greenwashing, and the need for alignment across diverse perspectives. A co-creation session further refined these insights, leading to the development of the Tactical Sustainability Cards—a tool designed to inspire sustainable thinking, guide decision-making, and foster collaboration. The Tactical Sustainability Cards were validated through expert feedback and iterative refinement, emphasising their utility in overcoming limitations of existing Design for Sustainability (DfS) tools, such as complexity and narrow focus. By providing actionable prompts and a shared language, the cards empower designers to navigate sustainability challenges, align stakeholders, and justify sustainable initiatives effectively. This research contributes to bridging the gap between sustainability theory and practice by offering a practical tool that integrates sustainability into design processes. The findings lay a foundation for future work exploring the broader applicability of the cards and elaborate on the potential for design to harmonise innovation and sustainability, addressing the environmental and societal challenges.