Blastocyst complementation enables the generation of donor pluripotent stem cell (PSC)-derived tissues in vivo, but its application has largely been limited to individual organs. Here, we establish epiblast complementation, a robust strategy for generating mice from donor PSCs. By creating an empty developmental niche in the host epiblast, we show that both wild-type and genetically modified naive PSCs can fully replace the host epiblast, contribute to all epiblast-derived tissues, and generate live offspring. Formative PSCs can also fully reconstitute the epiblast and support development to term, demonstrating developmental potential comparable to that of naive PSCs. Notably, a single naive PSC is sufficient to reconstitute the epiblast and give rise to live offspring. Together, these findings establish epiblast complementation as a functional assay for assessing PSC developmental potential and provide a strategy for generating genetically defined animals directly from cultured PSCs.