Helper innate lymphoid cells (ILCs), comprising groups ILC1, ILC2, and ILC3, possess unique advantages in eliciting rapid immune responses and were recently found to exhibit direct tumor-killing capacities comparable with those of cytotoxic ILCs [natural killer (NK) cells] in humans and mice. Although ILCs are primarily tissue-resident cells, their role in the hematopoietic system is increasingly being recognized. This review provides an overview of ILC ontogeny, as well as the physiological and pathological roles of these cells within the human and murine hematopoietic systems. We recapitulate recent advancements regarding ILC embryonic hematopoietic origin and the dynamic interactions between ILCs and leukemic cells or other immune cell populations, highlighting the dual roles ILCs can play in carcinogenesis. Exploring the functional potential of ILCs can inform the design of rational immunotherapeutic strategies against hematological malignancies.