Embryonic hematopoiesis is thought to occur exclusively in the extraembryonic yolk sac before hematopoietic stem cells (HSCs) arise in the aorta-gonad-mesonephros region. Here we identify a previously unrecognized hematopoietic site at the maternal-fetal interface in mice, termed MIXER (Maternally Interfaced eXtraEmbRyonic) tissue, which develops contemporaneously with the yolk sac and exhibits robust hematopoietic activity. MIXER contains abundant hematopoietic precursors, including classical CSF1R+ erythro-myeloid progenitors and a unique embryonic CD4+CSF1R- Erythro-Myeloid PRogenitOR (eEMPROR) population. Lineage-tracing experiments demonstrate that eEMPROR cells contribute to select macrophage subpopulations during fetal development, primarily in the perivascular space. Notably, early human placental villi, before HSC emergence, also harbor CD4+ nucleated erythrocytes, indicating a conserved hematopoietic role for the maternal-fetal interface. These findings establish MIXER as an anatomically distinct niche for embryonic hematopoiesis and expand the developmental map of blood cell emergence in mammals.