This study examined how person–supervisor fit is related to employees’ proactive behavior and unethical behavior towards the organization. The study involved 321 employees representing various sectors in Poland. The participants completed the Person–Supervisor Fit Scale, Proactive Behavior Scale, and the Unethical Behavior Questionnaire. Results show that a supplementary fit is weakly and positively related to proactive behavior but is not related to complementary fit. Surprisingly, supplementary fit is weakly but positively related to unethical behavior, while complementary fit from a needs–resources perspective is weakly and negatively associated with unethical behavior. Conclusions may be applied to organizational settings challenged by the problem of employee unethical behavior and their low proactivity in the context of person–supervisor congruence.