Background: In patients with immune thrombocytopenia (ITP), a critical bleed such as intracranial hemorrhage or bleeding causing hemodynamic instability, requires urgent treatment to rapidly raise the platelet count and restore hemostasis. There is no standardized approach to this hematological emergency. Objective: The McMaster ITP Emergency Management Guideline Group developed evidence-informed recommendations for the management of a critical bleed in adults and children with ITP. Methods: The guideline panel included 5 clinical experts in adult ITP, 3 clinical experts in pediatric ITP, 2 emergency department physicians, 1 emergency department nurse, 2 methodologists, and 4 patient partners. To inform recommendations, the guideline team conducted a multicentre retrospective cohort study and systematic reviews. The panel used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach to rate the certainty of evidence and GRADE's evidence-to-decision framework to formulate recommendations. Results: Given the life-threatening nature or significant morbidity associated with the condition, despite low or very low certainty evidence, the panel made strong recommendations for the combined use of high-dose corticosteroids, high-dose intravenous immunoglobulin (IVIG), platelet transfusions, tranexamic acid, and thrombopoietin receptor agonists (TPO-RAs) for the treatment of adults or children with a critical ITP bleed. The panel made a conditional recommendation for urgent splenectomy when other treatments have failed and, due to the risk of thrombosis, a conditional recommendation against the use of recombinant factor VIIa. Conclusions: Motivated by the life-threatening nature of the condition, the panel made strong recommendations for the combined use of high-dose corticosteroids, high-dose IVIG, platelet transfusions, tranexamic acid, and TPO-RAs for the emergency management of adults and children with a critical ITP bleed.