Teacher solidarity co-design is a special case of participatory design research that emphasizes the unique power dynamics of partnering with teachers who are multiply positioned in schooling, educational policy and research, and society. Through contrastive case analysis of four instrumental cases, five principles that characterize teacher solidarity co-design emerged. Collectively, the cases traverse the professional life-course of teachers in a variety of contexts but foreground co-learning and relationality between teachers and researchers in their efforts to create transformational change in schools. Additionally, the analysis of the cases centers our own experiences and insights as former teachers who are currently educational researchers. The principles account for the complex and nested systems of power that teachers occupy within efforts that seek to transform schools into more equitable and just spaces.