Congenital heart disease originates at least in part from genetic defects altering the development and maturation of the heart, and the role of protein modifiers in this process is not understood. The ubiquitin-like protein NEDD8 modifies proteins in a way similar to ubiquitin, termed neddylation, and requires NEDD8-specific E1 (NAE), E2 (Ubc12), and E3 ligases. Through regulating the function of protein targets, neddylation participates in diverse cellular processes and pathophysiological events. At the moment, it is not known whether or not neddylation plays a role in heart development. Here we report a previously unrecognized role of neddylation in early cardiogenesis and embryonic viability. Neddylation is activated in embryonic mouse hearts, but downregulated in adult hearts. Germline knockout (KO) of NAE1, a regulatory subunit of NAE, leads to embryonic lethality prior to E10.5, suggesting a critical role in early embryonic development. Mice with cardiac progenitor cell-specific (Nkx2.5Cre/+::NAE1flox/flox) KO of NAE1 exhibited severe cardiac effusion, bloody amniotic effusion, diffuse hemorrhage, and embryonic lethality by E12.5. Mice with cardiomyocyte (CM) and vascular smooth muscle cell (SMC)-specific (SM22aCre/+::NAE1flox/flox) KO of NAE1 displayed cardiac hypoplasia, vascular wall thinning, and embryonic lethality by E14.5, which is accompanied by diminished CM and SMC proliferation. RNA-seq analysis revealed that these developmental abnormalities are associated with dysregulation of Notch signaling, a highly conserved pathway crucial to cell fate determination and differentiation during cardiac development. qPCR analysis showed that the expression of Notch targets was inhibited in NAE1-deficient hearts. In cultured cells, genetic or pharmacological inhibition of neddylation repressed the activity of a Notch luciferase reporter and the expression of Notch targets at transcript and protein levels, while overexpression of NICD (Notch intracellular domain) attenuated the inhibitory effect. Taken together, our in vivo and in vitro data indicate a novel role for neddylation in regulating Notch signaling and embryonic cardiac development. Future investigation is warranted to delineate the underlying mechanisms.