Bromodomain and extraterminal (BET) proteins are epigenetic readers that interact with acetylated lysines of histone tails. Recent studies have demonstrated their role in cancer progression because they recruit key components of the transcriptional machinery to modulate gene expression. However, their role during embryonic development of the pancreas has never been studied. Using mouse embryonic pancreatic explants and human induced pluripotent stem cells (hiPSCs), we show that BET protein inhibition with I-BET151 or JQ1 enhances the number of neurogenin3 (NEUROG3) endocrine progenitors. In mouse explants, BET protein inhibition further led to increased expression of β-cell markers but in the meantime, strongly downregulated Ins1 expression. Similarly, although acinar markers, such as Cpa1 and CelA, were upregulated, Amy expression was repressed. In hiPSCs, BET inhibitors strongly repressed C-peptide and glucagon during endocrine differentiation. Explants and hiPSCs were then pulsed with BET inhibitors to increase NEUROG3 expression and further chased without inhibitors. Endocrine development was enhanced in explants with higher expression of insulin and maturation markers, such as UCN3 and MAFA. In hiPSCs, the outcome was different because C-peptide expression remained lower than in controls, but ghrelin expression was increased. Altogether, by using two independent models of pancreatic development, we show that BET proteins regulate multiple aspects of pancreatic development.