Research on the relationship between proactive personality and turnover has yielded inconsistent results (i.e., positive, negative, and non-significant relationships). Using the boundaryless and protean career perspectives, we conducted two empirical studies among Chinese employees to reconcile the discrepancies in the literature by testing both the staying and leaving paths between proactive personality and turnover intention/behavior and exploring the moderating role of protean career orientation. The results of Study 1 (N = 148) showed that employees’ proactive personality (Time 1) had a negative indirect effect on turnover intention (Time 3) through internal employability (Time 2) and a positive indirect effect through external employability (Time 2). The results of Study 1 also suggested that internal and external employability offered a more coherent and powerful explanation for the mixed relationship between a proactive personality and turnover intention than other mediators (career satisfaction, internal networking, and external networking). Study 2 (N = 188) controlled for the effects of baseline turnover intention (Time 1) and adopted turnover behavior (Time 3) as the outcome variable predicted by employee proactive personality (Time 1). The results replicated the contrasting mediating effects of internal and external employability (Time 2) and revealed that protean career orientation strengthened the indirect positive effect of proactive personality on turnover behavior through external employability. These studies provide a more comprehensive view of the contrasting effects of a proactive personality on turnover and have important implications for talent retention in a boundaryless career world.