Introduction: The pandemic disrupted daily lives and negatively affected psychological factors such as perceived security, social relations, distancing, stress, and engagement. Yet, empirical insights are still largely lacking of the complex evolving interplay of changing everyday mobilities and physical activities, accessibility perceptions, and mental health outcomes during and after the pandemic. This study explores how travel, physical activity and perceived accessibility affect mental health during the COVID-19 crisis. Method: Drawing on 2020, 2021 and 2022 panel survey data from residents of Greater Oslo, Norway, we (i) develop a theoretical framework on the interplay between travel and behaviour, perceived accessibility and mental health, (ii) we set up measurement instruments to capture key outcomes (Perceived Accessibility Scale, and Mental Health Index), and (iii) test the interplay using panel survey data from before, during, and immediately after the pandemic analysed in Structural Equation Models. Results: Substantial negative pandemic impacts on trip frequencies, public transport shares and accessibility perceptions are observed, the latter with important mediating effects on mental health. Physical activity levels and mental health were initially also negatively affected, but less so than travel and perceived accessibility and they also rebounded back to normal during the study period. Pandemic impacts on travel, perceived accessibility and mental health turned out to be uneven, with for instance stronger impacts for women than for men. Conclusions: The findings highlight the central role of perceived accessibility as a mediating factor between travel behaviour and mental health, underscoring its importance in transport policy and planning. The unequal impacts of the pandemic across socio-demographic groups, especially for women, demonstrate the need for more inclusive and resilient mobility systems. Moreover, the study illustrates the value of using subjective, longitudinal measures to understand how mobility and well-being are interlinked over time, particularly in response to societal disruptions like the pandemic.