The Hippo pathway governs cellular differentiation, morphogenesis, and homeostasis but how it regulates these processes in lymphatic vessels is unknown. Therefore, I aimed to reveal the role of the final effectors of the Hippo pathway, YAP and TAZ (YAP/TAZ), in lymphatic endothelial cell (LEC) differentiation, morphogenesis, and homeostasis in vivo and in vitro. During mouse embryonic development, LEC-specific depletion of Yap/Taz disturbed both plexus patterning and valve initiation with upregulated Prox1. Conversely, LEC-specific YAP/TAZ hyperactivation impaired lymphatic specification and restricted lymphatic sprouting with profoundly downregulated Prox1. Notably, lymphatic YAP/TAZ depletion or hyperactivation aggravated or attenuated pathologic lymphangiogenesis in mouse cornea. Mechanistically, VEGF-C activated canonical Hippo signaling pathway in LECs. Indeed, repression of PROX1 transcription by YAP/TAZ hyperactivation was mediated by recruitment of nucleosome remodeling and histone deacetylase (NuRD) complex and endogenous binding activity of TEAD to the PROX1 promoter. Furthermore, YAP/TAZ hyperactivation enhanced MYC signaling and inhibited CDKN1C, leading to cell cycle dysregulation and aberrant proliferation. I find that YAP/TAZ play promoting roles in remodelling lymphatic plexus patterning and postnatal lymphatic valve maintenance by negatively regulating Prox1 expression. I further show that YAP/TAZ act as plastic regulators of lymphatic identity and define the Hippo signaling-mediated PROX1 transcriptional programming as a novel dynamic checkpoint underlying lymphatic endothelial cell plasticity and pathophysiology.