Naïve and primed pluripotent states retain distinct molecular properties, yet limited knowledge exists on how their state transitions are regulated. Here, we identify Mettl3, an N6-methyladenosine (m6A) transferase, as a regulator for terminating murine naïve pluripotency. Mettl3 knockout pre-implantation epiblasts and naïve embryonic stem cells (ESCs) are depleted for m6A in mRNAs and yet, are viable. However, they fail to adequately terminate their naïve state, and subsequently undergo aberrant and restricted lineage priming at the post-implantation stage, leading to early embryonic lethality. m6A predominantly and directly reduces mRNA stability, including that of key naïve pluripotency promoting transcripts. This study highlights a critical role for an mRNA epigenetic modification in vivo, and identifies regulatory modules that functionally influence naïve and primed pluripotency in an opposing manner. Overall design: polyA RNA-seq was measured in mouse embryonic stem cells (ESCs) and embroid bodies (EBs), each in WT and in Mettl3-KO cell lines. RNA-seq was measured also from WT mouse embronic fibroblasts (MEF). 3 biological replicates are available from ESCs and 2 from EBs. Replicate C in ESCs was measured alongside protein levels (SILAC) and was used for the analysis of that assay.