In the current dynamic and flexible work environment, traditional career models are constantly challenged by individuals’ self-concepts of career development. Previous studies have investigated the predictors of subjective career success, yet little is known about the impact of proactive career orientation on subjective career success. This study, grounded in the career construction theory, aims to examine the influence mechanism of proactive career orientation on subjective career success by analyzing questionnaire data from 296 employees. Empirical results indicate that proactive career orientation has a positive impact on subjective career success. Second, career adaptability partially mediates the relationship between proactive career orientation and subjective career success. Third, mentoring moderates the relationship between proactive career orientation and career adaptability, as well as the relationship between career adaptability and subjective career success. Specifically, both the positive impact of proactive career orientation on career adaptability and the positive impact of career adaptability on subjective career success are stronger when the level of mentoring is higher. Fourth, the indirect relationship between proactive career orientation and subjective career success through career adaptability is stronger when mentoring is high compared to when mentoring is low. This study contributes to the career construction theory by identifying the influence mechanism of proactive career orientation on subjective career success through career adaptability, with mentoring moderating the process. As for practical implications, research findings remind managers of the importance of career planning and mentorship in enhancing employees’ subjective career successes.