The purpose of this study was to investigate external whistleblowers’ experiences of workplace bullying by superiors and colleagues, and to analyze how the bullying was influenced by factors such as the support they received from government or NGOs, and whether colleagues understood the reasons for the whistleblower’s actions. For bullying by colleagues we also examined to what extent this was influenced by superiors’ behavior towards the whistleblower. We reviewed the relevant literature on workplace bullying and whistleblowers’ experiences of negative or retaliatory actions and developed three hypotheses, which we tested using data gathered from Korean external whistleblowers. Results revealed that external whistleblowers experienced work-related bullying by superiors and social relation-related and person-related bullying by colleagues more frequently, and found it more distressing, than other types of workplace bullying. Superiors’ bullying was a dominant factor affecting bullying by colleagues. Colleagues’ understanding of the reason for the whistleblower’s actions was significant in reducing bullying frequency while support from government and NGOs was not significant in reducing it. Based on these findings, practical implications are discussed.