Public perceptions of whistleblowers are polarized: While some praise them as heroes, others view them as traitors. We argue that polarized moral judgments stem from motives attributed to the whistleblower. To test this, we first identified relevant motive attributions in whistleblowing situations via a qualitative study (N = 201). Participants read a whistleblowing scenario and were asked which motives they attributed to the actor. Coding of open-ended responses revealed four main motive attributions: prosocial, competitive, individualistic, and deontic. In a second study with a similar scenario (N = 125), we then developed and validated a self-report scale capturing the four motive attributions. In a third scenario study (N = 742), we manipulated the type of whistleblowing (no, internal, external, or public whistleblowing) and found that the type of whistleblowing affected judgments of the whistleblower’s moral character and that this relationship was mediated by prosocial, competitive, and deontic motive attributions.