Regular physical activity (PA) can address many of the negative side effects experienced by individuals following cancer treatment and support the optimization of physical and psychosocial well-being. However, many survivors of cancer are not sufficiently active to achieve these health benefits. The purpose of this study was to describe the development of a physical activity behavior change (PABC) intervention, MedEx IMPACT (IMprove Physical Activity after Cancer Treatment), which aims to increase cancer survivors’ PA levels. A review of the literature and focus groups with survivors of cancer were conducted in order to generate recommendations to inform the intervention development process. This process was guided and informed by: (1) the Medical Research Council’s (MRC) framework for the development, evaluation, and implementation of complex interventions, (2) the Behaviour Change Wheel (BCW), and (3) the Theoretical Domains Framework (TDF). Recommendations for strategies to support habitual PA and adherence to community-based exercise programs, generated by survivors of cancer who participated in 7 focus groups (n ¼ 41), were synthesized with 13 statements of findings that were generated from 10 studies included within the review of the literature. Detailed mapping exercises are presented which outline the link between these sources, the MRC framework, the BCW and TDF, and the intervention content. MedEx IMPACT is the first PABC intervention for survivors of cancer to be developed through the application of the MRC framework, BCW, and TDF. The next phase in this research is to test the acceptability and effectiveness of MedEx IMPACT.