The medical field has extensively investigated the impact of sedentary behavior and physical activity, recognizing them as distinct entities with separate effects on the body. As opposed to physical activity, sedentary behavior refers to activities that involve minimal movement and low energy expenditure. Growing medical evidence has consistently associated excessive sedentary behavior with an increased risk of chronic health conditions. The solution to this problem is to have frequent breaks from prolonged sitting. The workplace has been recognized as a setting where prolonged sedentary behavior is frequently observed. Office workers often struggle to reduce their sitting time due to the prolonged hours spent in desk-based jobs. Hence, the aim of this study is to determine the essential design requirements for a behavior change support system that promotes regular breaks from prolonged sitting and encourages desk-based workers to engage in walking or stretching exercises. To accomplish this objective, we implemented various user-centered design techniques. The aim was to identify any usability and functionality issues, privacy concerns, information sharing, data visualization, and content-related problems that may arise. Drawing from the input provided by office workers, several key factors surfaced as essential in reducing sedentary behavior within the workplace environment, utilizing a behavior change support system via the smartphone application. These factors include integrating contextual awareness, ensuring accurate and reliable data, highlighting the health consequences of sedentary behavior, offering data transparency, and implementing effective privacy management. Incorporating these elements into the design of a behavior change support system is essential for promoting healthier and less sedentary behavior for office workers.