De novo variants affecting the core complex required for monoubiquitination of histone H2B (H2Bub1) are enriched in human congenital heart disease. H2Bub1 is an enigmatic chromatin modification required in stem cell differentiation, cilia function, post-natal cardiomyocyte maturation and transcriptional elongation. However, it is still unknown how H2Bub1 affects cardiogenesis (heart structure formation), which is distinct from cardiomyocyte maturation and underlies congenital heart disease. Here we show that the RNF20-core complex (RNF20-RNF40-UBE2B) is required for cardiogenesis in mouse embryos and is essential for differentiation of human iPSCs into cardiomyocytes. Mice with cardiac-specific deletion of Rnf20 are e12.5 lethal, have thinned myocardium, a deficient ventricular septum, and abnormal cardiac sarcomere organization. We analyzed H2Bub1 marks during the time course of differentiation of human iPSCs into cardiomyocytes, and demonstrated that H2Bub1 marks are erased from a majority of genes at the transition from cardiac mesoderm to cardiac progenitor cells, but are preserved on a subset of long cardiac-specific genes. Sarcomeric gene expression is dependent on normal H2Bub1 both in mice and in human iPSC-derived cardiomyocytes. Finally, we identify an accumulation of H2Bub1 near the center of tissue-specific genes in human cardiomyocytes, mouse embryonic fibroblasts, and human fetal osteoblasts associated with transcriptional elongation efficiency that is absent in UBE2B knock-out H2Bub1-deficient cardiomyocytes. In summary, normal H2Bub1 distribution is required for cardiac morphogenesis and cardiomyocyte differentiation, and we propose that H2Bub1 regulates tissue-specific gene expression by increasing the efficiency of transcriptional elongation.