Objective Combining continuous positive airway pressure with physical activity (PA) might be a promising strategy to treat obstructive sleep apnea (OSA). This article describes how intervention mapping (IM) can guide the development, content, and mechanisms of action of a mobile application to promote PA in adults with OSA.Methods To develop the program, the IM approach was followed. This article presents the first three steps of IM to develop a mixed intervention (with interventionists and a digital application) aiming to: (1) assess patients’ health problems and needs in a literature review to determine their expectations and perceived facilitators and barriers to PA behavior change and thus select the determinants of behavior; (2) formulate the expected intervention outcomes and objectives to be met to achieve the overall program goals; and (3) select and implement the behavior change techniques (BCTs) to achieve the change objectives.Results The literature review identified the relevant determinants (e.g., self-efficacy, coping, planning, and habit) of PA behavior using the health action process approach and multiprocess action control. These results were used to specify the program outcomes for PA adapted to physical, psychological, and social parameters. Overall, 11 performance objectives and 30 change objectives were defined. Lastly, BCTs and practical applications were identified.Conclusions The study provides a theoretical and methodological basis for researchers and practitioners given the current paucity of evidence-based PA interventions for adults with OSA. It addresses the lack of BCTs (framing and prompts/cue techniques) and meaningful behavioral determinants (identity and habit) in most interventions.