Since teacher research engagement is increasingly sought as a widespread practice, there is a need to pay more attention to the positive trajectories of research-engaged teachers that already exist. This qualitative interview-based study explores what factors motivate and sustain teacher research engagement via focusing on narratives of 36 teachers in Poland and Spain who are successfully research-engaged beyond their own formal education requirements. The study finds that teacher research engagement entails a complex interplay between: intrinsic and extrinsic motivations, originating mainly from teachers’ own personal and professional desires; personal characteristics and skills, especially inner need and willingness; and environmental factors, both inside and outside their schools. The study offers concrete lessons and specific recommendations upon which diverse stakeholders – i.e., teacher educators, researchers, continuing professional development providers, headteachers, and teachers – can support teachers in becoming and remaining research-engaged throughout their careers.