Design-based learning (DBL) has been considered a useful approach in teacher education because of its emphasis on the investigation of technology integration problems in design processes. Despite recent interest in understanding how technological, pedagogical, and content knowledge (TPACK) translates to action, limited research exists on how TPACK is developed within DBL contexts and what principles of DBL can be applied to TPACK development. To address these critical gaps in the literature, an approach was developed that outlined eight DBL principles that foster understanding of TPACK-in-action in teacher education contexts. Next, a graduate course was designed to determine how course activities facilitated understanding of TPACK-in-action and to what extent students enacted TPACK-DBL principles. Following a case study methodology, data were collected from 10 graduate students through reflection reports, design guides, and researcher observation notes. The analysis of qualitative and descriptive data revealed that as a result of TPACK-DBL activities, students developed a four-dimensional understanding of TPACK-in-action: theory-practice connection, readiness for practice, technological proficiency, and sustainable learning of TPACK. The results offer recommendations to teacher educators for developing understanding of TPACK-in-action through DBL activities.