As office workers have the autonomy of locations due to the advance of technology and the changes in socio-economic contexts, mobility within the workplace is noticeably increased. In the flexible workplace, working locations are not tied to the physical workstations of offices and are rather decided by office workers according to their preference for working environments. However, the current building simulation tools do not reflect the new behavioral patterns of increasingly mobile workers and typically assume sedentary behavior at the fixed seats for the uniform working hours, from 9 am to 5 pm. As the occupancy schedule has impacts on the accuracy of building performance simulation, understanding occupant behavior is key to ultimately increasing the building performance and enhancing the comfort and satisfaction of office workers in the workplace.In this research, the visual environment was investigated because working is a cognitively demanding activity associated with the visual perception of built environments. Although there are daylight metrics and criteria for lighting conditions in the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) standards and Leadership in Energy and Environmental Design (LEED) certificates, they can be obsolete in the highly-mobile workplace, such as Activity-base Workplace (ABW) and non-territorial workplace. The increased mobility within the workplace has not been constructively addressed in Indoor Environmental Quality (IEQ) assessments. The current assessments are typically based on floor areas rather than on the seats and mostly rely on desk-level illuminance levels, which are not necessarily associated with the visual experience of workers working on laptops. Also, the previous studies in human behavior, including Post Occupancy Evaluation (POE) studies, have oversimplified the qualities of visual environments and collected the response data from occupants in a sporadic timeframe, which does not align with the frequent changing rates of visual environments. The field of Built Environment needs new tools in order to examine these new behaviors with frequent or even real-time data collection. Seat selection is a way of communication between occupants and built environments and also a measurable aspect of mobility in the workplace. It is particularly practical to be measured quantitatively at frequent intervals with the deployment of occupancy sensors without intervening activities of occupants. Investigation of seat selection behavior helps understand the preference of occupants in the built environments mediately because occupants are likely to position themselves where they feel comfortable with the environmental conditions. A better understanding of seat selection can provide insight into the gaps in the current assessment methods and in the environmental behavioral research in the built environment. This research suggested a method to examine the relationship between seat selection behavior and visual environments in the highly mobile workplace. The method was explored through three studies: 1) the association between seat selection and visual environmental qualities, 2) the perception of seat-specific visual experience, and 3) the reconsideration of the current daylight metrics in building simulation. This research was conducted as an experimental study with 47 participants (33 females, 13 males, and 1 non-binary). There were 3 sessions per day (9 am, 12 pm, 3 pm) for 5 days (15 sessions in total), and each session was executed for 100 minutes with 2 to 4 participants (M = 3.13) in four different spaces that had homogeneous seat settings. In the first part, Study #1 found that illuminance level on the eye, daylight glare probability (DGP), and distance to the side walls were the main predictors of seat selection behavior. This finding contradicts the conventional method in the building simulation, that the illuminance level on the desk is being used as the primary criterion. In the second part, Study #2 found that the illuminance on the eye was positively associated with the perception of overall brightness, whereas the illuminance level on the screen was closely associated with the perception of glare. This supports the findings of Study #1, which demonstrated that the illuminance level on the eye is more influential than the level on the desk. In the last part, Study #3 questioned the efficacy of current daylight metrics: Useful Daylight Illuminance (UDI) and Daylight Glare Probability (DGP). The findings indicated that the concept of useful daylight (between 300 lux and 2000 lux) was not particularly associated with the perceived level of visual comfort and that there was no significant correlation between the DGP value and the perceived level of visual comfort. These findings suggest that the current daylight metric needs to be updated for the highly mobile workplace. New working behavior requires new workplace designs with updated assessment tools for better building performance and higher user satisfaction. This study demonstrated the relationship between seat selection and visual environments and emphasized the necessity of seat-based daylight metrics for the highly mobile workplace. The findings also highlighted the potential replacement of survey tools with seat selection detection and sensor deployment in POE and the integration of human behavior study and building performance simulation, which can further simplify the environmental data collection. In a further study, this method can be adopted for thermal comfort analysis and used for the prediction of occupancy schedules based on real-time indoor environmental conditions.