Granulocyte-monocyte progenitors (GMPs) have been previously defined for their potential to generate various myeloid progenies such as neutrophils and monocytes. Although studies have proposed lineage heterogeneity within GMPs, it is unclear if committed progenitors already exist among these progenitors and how they may behave differently during inflammation. By combining single-cell transcriptomic and proteomic analyses, we identified the early committed progenitor within the GMPs responsible for the strict production of neutrophils, which we designate as proNeu1. Our dissection of the GMP hierarchy led us to further identify a previously unknown intermediate proNeu2 population. Similar populations could be detected in human samples. proNeu1s, but not proNeu2s, selectively expanded during the early phase of sepsis at the expense of monocytes. Collectively, our findings help shape the neutrophil maturation trajectory roadmap and challenge the current definition of GMPs. Display omitted •GMPs are heterogeneous at the transcriptomic and proteomic level•An early committed neutrophil progenitor (proNeu1) exists within GMPs•proNeu1 gives rise to proNeu2, sequentially differentiating into mature neutrophil•proNeu1 specifically expands during emergency granulopoiesis The daily production of circulating neutrophils depends on committed and proliferative progenitors, but the ontogenic pathway of neutrophil progenitors remains poorly defined. Integrating multiple single-cell-based technologies, Kwok et al. resolve GMP heterogeneity to identify an early committed neutrophil progenitor (proNeu1) and map out the entire neutrophil developmental pathway in steady state and emergency granulopoiesis.