IntroductionActive travel is an accessible form of physical activity, associated with physical and mental health benefits, particularly for older adults. This study aimed to identify the behavioural determinants that significantly impact older adults’ engagement in active travel as well as how and why these behavioural determinants occur. MethodsThis study employed an explanatory sequential mixed methods design informed by the Theoretical Domains Framework (TDF). The study focused on older adults in Scarborough, Canada. In the quantitative phase, a TDF-informed survey was distributed among Scarborough older adults and analyzed using descriptive statistics, Chi-squared tests, and generalized linear models. TDF determinants that significantly impacted older adult participants in active travel were identified. The qualitative phase followed up with select survey participants about their experiences with these TDF determinants. Semi-structured interviews were conducted, and data was analyzed using thematic codebook analysis. To integrate the quantitative and quantitative results, data were interpreted and integrated using a joint display matrix. ResultsThe survey results suggest that the TDF domains of motivation (i.e., feeling inspired to active travel) and skill (i.e., having the aptitude to active travel) were highly predictive of active travel behaviour among older adults in Scarborough, Canada. Beyond the TDF, the likelihood of active travel increased if participants reported being encouraged and satisfied with their health, fitness, exercise, and well-being in general. The interview results suggest that fostering motivation and skill require a network of interventions that address multiple TDF domains such as promoting action planning, creating commitment, building social connectedness, increasing awareness of active travel options, and building emotional and physical safety. By integrating the quantitative and qualitative results, three overarching themes were presented about older adults’ needs to engage in active travel: building reassurance (i.e., putting safety first); building meaningfulness (i.e., creating joy, fulfillment, and purpose); and building relatedness (i.e., creating awareness and connection). ConclusionsThis study suggests several important implications for future research and policy. The results of this study provide evidence to support investment in both built environment improvements (e.g., safer intersections, bike lanes, lower vehicle speed limits, public transit subsidies) as well as tailored activities to promote active travel (e.g., public awareness campaigns, skill development activities, organized walks). The mixed methods study design employed in this study in conjunction with a novel application of the TDF allowed for a more thorough understanding of behavioural determinants of active travel among older adults.