Although extroversion and proactive personality are related to career success, the mechanisms through which the relationships occur are unclear. Based on the contest- and sponsored-mobility processes, we examine a model linking extroversion and proactive personality to career success through the mediating effects of mentoring received and organizational knowledge. We also theorize that mentoring provides learning opportunities, which result in greater organizational knowledge, that contribute to career success. Results, from a sample of 333 employees with a diverse set of occupations, indicated that the relationships of proactive personality and extroversion with objective and subjective measures of career success were mediated by mentoring received and organizational knowledge. Additionally, mentoring received influenced organizational knowledge, and both were related to objective and subjective measures of career success. Our study provides insight into how personality influences career success and provides support for both contest- and sponsored-mobility models of career success.