The evolving nature of contemporary careers has sparked an interest in the sustainability of individual careers, which encompasses the pursuit of careers in a manner that promotes health, productivity, and overall happiness. Although previous studies have provided valuable perspectives on sustainable careers, there remains a notable lack of evidence regarding the interplay between individual and contextual determinants in crafting sustainable careers. Therefore, integrating the framework of sustainable careers with the Conservation of Resources (COR) theory, this study proposes a serial indirect effect mechanism that examines the relationship between contextual determinants (i.e., work/family demands and resources) and career sustainability indicators (i.e., work-family balance, employability, work engagement, and work strain) sequentially through career crafting and person-career fit. A two-wave time-lagged survey was conducted with 412 employees from Turkey. Hierarchical regression analyses were performed to test the proposed model, while Process Macro analyses were conducted to examine the serial indirect effects. Results showed that contextual demands and resources were positively associated with career crafting and such career initiatives were related to optimized person-career fit and career sustainability indicators. Notably, contextual determinants were indirectly related to employability and work engagement serially via career crafting and person-career fit. Highlighting the importance of a whole-life perspective in career development, which involves work and family contexts, this study reveals the integral role of career proactivity and its interplay with contextual determinants in building sustainable careers.