Congenital heart disease (CHD) is present in 1% of live births, yet despite large-scale genomic sequencing efforts, identification of causal mutations remains a challenge. We hypothesized that genetic determinants for CHDs may lie in the protein interactomes of GATA4 and TBX5, two transcription factors whose mutation cause CHDs. Defining the GATA4 or TBX5 interactomes in human cardiac progenitors via affinity purification-mass spectrometry and integrating the results with genetic data from the Pediatric Cardiac Genomic Consortium revealed an enrichment of de novo variants associated with CHD. A consolidative score that prioritized interactome members based on variant, gene, and proband features identified likely CHD-causing genes, including the epigenetic reader GLYR1. GLYR1 and GATA4 widely co-occupied and co-activated cardiac developmental genes, and the GLYR1 missense variant identified disrupted interaction with GATA4 and impaired transcriptional co-regulation in cardiomyocyte differentiation in vitro and cardiogenesis in vivo. This integrative proteomic and genetic approach provides a framework for prioritizing and interrogating the contribution of genetic variants in disease.