Immune-checkpoint protein V-domain immunoglobulin suppressor of T-cell activation (VISTA) controls antitumor immunity and is a valuable target for cancer immunotherapy. This study identified a role of VISTA in regulating Toll-like receptor (TLR) signaling in myeloid cells and controlling myeloid cell–mediated inflammation and immunosuppression. VISTA modulated the polyubiquitination and protein expression of TRAF6. Consequently, VISTA dampened TLR-mediated activation of MAPK/AP-1 and IKK/NF-κB signaling cascades. At cellular levels, VISTA regulated the effector functions of myeloid-derived suppressor cells and tolerogenic dendritic cell (DC) subsets. Blocking VISTA augmented their ability to produce proinflammatory mediators and diminished their T cell–suppressive functions. These myeloid cell–dependent effects resulted in a stimulatory tumor microenvironment that promoted T-cell infiltration and activation. We conclude that VISTA is a critical myeloid cell–intrinsic immune-checkpoint protein and that the reprogramming of tolerogenic myeloid cells following VISTA blockade promotes the development of T cell–mediated antitumor immunity.