Using self-determination theory among a sample of student employees, the present cross-sectional study (N = 358) examines how mentors' interpersonal behaviors relate to both motivation at work and motivation for a mentoring relationship and how these two contexts of motivation can differentially relate to mentees' work outcomes. Results revealed that mentors' need-supportive interpersonal behaviors were associated with greater autonomous motivation at work and in the mentoring relationship and, in turn, to greater well-being and work engagement, and to lower turnover intentions. In contrast, need-thwarting interpersonal behaviors were associated with greater controlled motivation at work and in the mentoring relationship and, in turn, to lower well-being and work engagement, and to greater turnover intentions. Overall, this study illustrates the impact of the mentor-mentee relationship on motivation for work and for the mentoring relationship and provided support for the contribution of both motivational contexts in the work-related outcomes of employees in the workplace.