Inappropriate activation of the p53 transcription factor contributes to numerous developmental syndromes characterized by distinct constellations of phenotypes. How p53 drives exquisitely specific sets of symptoms in diverse syndromes, however, remains enigmatic. Here, we deconvolute the basis of p53-driven developmental syndromes by leveraging an array of mouse strains to modulate the spatial expression pattern, temporal profile, and magnitude of p53 activation during embryogenesis. We demonstrate that inappropriate p53 activation in the neural crest, facial ectoderm, anterior heart field, and endothelium induces distinct spectra of phenotypes. Moreover, altering the timing and degree of p53 hyperactivation substantially affects the phenotypic outcomes. Phenotypes are associated with p53-driven cell-cycle arrest or apoptosis, depending on the cell type, with gene expression programs, rather than extent of mitochondrial priming, largely governing the specific response. Together, our findings provide a critical framework for decoding the role of p53 as a mediator of diverse developmental syndromes. • Inappropriate p53 activation during embryogenesis triggers developmental defects • Spectrum of defects depends on degree and spatiotemporal pattern of p53 activation • p53 activation drives apoptosis and cell-cycle arrest in a context-dependent manner • Gene expression rather than mitochondrial priming dictates apoptotic responses Various developmental syndromes are associated with increased p53 activity. Bowen et al. generate a panel of mouse models to define how different spatial expression patterns, temporal profiles, and magnitudes of p53 activation during embryogenesis drive distinct spectra of developmental phenotypes. [ABSTRACT FROM AUTHOR]