The topic of proactivity has long captured the attention of career scholars, leading to fertile, yet often disconnected streams of inquiry on personality traits and behaviors that can help workers to advance their own careers, improve their work conditions, or access desired rewards. Based on a review of diverse approaches to conceptualizing and assessing proactive career behavior and related constructs, we identified seven commonly appearing behavioral categories and assembled a representative set of items of each category. An exploratory factor analysis in a sub-sample of adult workers ( n = 250) yielded three interrelated factors, labeled (a) planning/reflecting/reskilling (or looking ahead, e.g., engaging in self-reflection and skill development efforts); (b) networking/conferring (or looking to others, e.g., consulting with colleagues and supervisors); and (c) exploring/searching (or looking around, e.g., monitoring career options proactively). A bifactor model fit the data well in another sub-sample ( n = 337), suggesting that the three factors were subsumed by a larger construct, which we labeled career sustainability behavior. Results of a structural path analysis indicated that, along with supervisor support, proactive personality, and conceptually-relevant self-efficacy measures, engagement in career sustainability behaviors was predictive of perceived internal and external job marketability.