This is a pioneer study to examine the mechanism underlying the relationship between proactive personality and career adaptability. Using a moderated mediation approach, it tested the mediating effect of thriving on this relationship and the moderating effect of proactive personality on the relationship between thriving and career adaptability. Three hundred and sixty-four adult employees participated in the survey study. Results demonstrated that proactive personality first promoted individuals' thriving at work, which in turn led to improved career adaptability. In addition, the effect of thriving on career adaptability was found to be stronger for those individuals with low rather than high proactive personality. In supporting this, the moderated mediation analysis further indicated that low proactive individuals, compared to their high proactive counterparts, relied more on thriving when developing career adaptability resources. These findings have important implications for career research and career counseling practices.