The Dhaka Metro Rail (DMR) has been constructed as part of the Dhaka Transport Coordination Authority’s 20-year Strategic Transport Plan to reduce traffic congestion in Dhaka, the capital city of Bangladesh. The DMR is the first urban rail transit system in Bangladesh and has the potential to change the existing modal share. Commuters have mixed responses about the daily commuting on the DMR and mode choice behavior. This study analyses the commuters’ perception of a modal shift towards the DMR by applying the theory of planned behavior (TPB). The structural equation model (SEM) used environmental concern and socio-demographic factors as additional explanatory variables to improve the explanatory capability of the TPB. A questionnaire survey was administrated using an online survey and validated via an in-person interview to collect the commuters’ responses. The results reveal that environmental concern is the most significant contributor to commuters’ perceptions of a modal shift towards the DMR in Dhaka City, followed by the attitude and perceived behavioral control of the respondents. The findings offer valuable insights for the DMR and other mass rapid transit service operators for policy-making in Dhaka and other cities with similar socio-economic demographics in the world.