The nuclear receptors (NR) retinoid X receptors (RXRs) exert immunomodulatory functions to control inflammation and metabolism via homodimers and heterodimers with several other NRs including retinoic acid receptors. IRX4204 is a novel, highly specific RXR agonist in clinical trials that potently and selectively activates RXR homodimers but not heterodimers. Here, we show that in vivo IRX4204 was compared favorably with FK506 in abrogating acute graft-versus-host disease (GVHD), which was associated with inhibiting allogeneic donor T cell proliferation, reducing T helper 1 differentiation and promoting regulatory T cell (Treg) generation. Recipient IRX4204 treatment reduced intestinal injury and decreased IFN-γ and TNF-α serum levels. Transcriptional analysis of donor T cells isolated from intestines of GVHD mice treated with IRX4204 revealed significant decreases in transcripts regulating pro-inflammatory pathways. In vitro, inducible Treg differentiation from naïve CD4+ T cells was enhanced by IRX4204; in vivo, IRX4204 increased the conversion of donor Foxp3- T cells into peripheral Foxp3+ Tregs in GVHD mice. Using Foxp3 lineage tracer mice in which both the origin and current FoxP3 expression of Tregs can be tracked, we demonstrate that IRX4204 supported Treg stability. Despite favoring Tregs and reducing Th1 differentiation, IRX4204-treated recipients maintained graft-versus-leukemia responses against both leukemia and lymphoma cells. Notably, IRX4204 reduced in vitro human T cell proliferation and enhanced Treg generation in mixed lymphocyte reaction cultures. Collectively, these beneficial effects indicate that targeting RXRs with IRX4204 could be used as a novel approach to prevent acute GVHD in the clinic.