The next generation of obesity medicines harness the activity of the glucose-dependent insulinotropic polypeptide and glucagon-like peptide 1 receptors (GIPR and GLP-1R), but their mechanism of action remains unclear. Here, we report that the GIPR is enriched in oligodendrocytes and GIPR signaling bidirectionally regulates oligodendrogenesis. In mice with adult-onset deletion of GIPR in oligodendrocytes, GIPR agonism fails to enhance the weight-loss effects of GLP-1R agonism. Mechanistically, GIPR agonism increases brain access of GLP-1R agonists, and GIPR signaling in oligodendrocytes is required for this effect. In addition, we show that vasopressin neurons of the paraventricular hypothalamus are necessary for the weight-loss response to GLP-1R activation, targeted by peripherally administered GLP-1R agonists via their axonal compartment, and this access is increased by activation of the GIPR in oligodendrocytes. Collectively, our findings identify a novel mechanism by which incretin therapies may function to promote synergistic weight loss in the management of excess adiposity.