Quiescence acquisition of proliferating neural stem cells (NSCs) is required to establish the adult NSC pool. The underlying molecular mechanisms are not well understood. Here, we showed that conditional deletion of the m(6)A reader Ythdf2, which promotes mRNA decay, in proliferating NSCs in the early postnatal mouse hippocampus elevated quiescence acquisition in a cell-autonomous fashion with decreased neurogenesis. Multimodal profiling of m(6)A modification, YTHDF2 binding, and mRNA decay in hippocampal NSCs identified shared targets in multiple transforming growth factor β (TGF-β)-signaling-pathway components, including TGF-β ligands, maturation factors, receptors, transcription regulators, and signaling regulators. Functionally, Ythdf2 deletion led to TGF-β-signaling activation in NSCs, suppression of which rescued elevated quiescence acquisition of proliferating hippocampal NSCs. Our study reveals the dynamic nature and critical roles of mRNA decay in establishing the quiescent adult hippocampal NSC pool and uncovers a distinct mode of epitranscriptomic control via co-regulation of multiple components of the same signaling pathway.