Recent digitization and technological advancements have given rise to gig work facilitated by digital platforms. In this exploratory study, we adopted the sustainable career perspective to explore how personal and contextual factors influence the work experiences of gig workers. Based on the qualitative data from two waves (2018-2019 and 2023) of in-depth interviews with 46 North American teachers who worked for ABCKID, one of the world’s largest online teaching platforms based in China, we found the evidence of personal agency in making gig work a long-term career choice beyond a short-term basis. Our study showed that contextual factors at the organizational- and institutional-level, such as job design, management practices and policies, as well as professional norms and national regulations, impacted the viability of the teachers’ platform careers. Our results highlight the importance of gig workers’ agency in actively engaging in career management behavior and devising strategies to cope with the changes in contextual factors so that the gig work could be sustained as a long-term career. Our study has implications for theory, practice, and public policy.