Fostering customer green purchase behavior is a fundamental constituent of an eco‐friendly hospitality firms' success. The present study developed a theory of green purchase behavior (TGPB) that clearly and sufficiently explains customer environmentally responsible buying behavior for green hospitality products, such as green hotels and green restaurants. Mixed methods based on a psychometric approach were used for the development of the theory. Within the theory, attitude, ascribed responsibility, and social norm directly activate the personal norm. These types of activators form based on awareness of consequences, image, ecological worldview, and environmental value. In addition, past behavior increases behavior. This theorization is fully supported and demonstrated through both qualitative and quantitative processes. Green purchase behavior was satisfactorily accounted for by the proposed theory. The TGPB included a stronger prediction power than the existing pro‐social theories, and it is applicable to diverse hospitality/tourism/consumer behavior contexts.