AbstractPlasmopara viticola, the causal organism of grapevine downy mildew, secretes a vast array of effectors to manipulate host immunity. Previously, several cell death‐inducing PvRXLR effectors have been identified, but their functions and host targets are poorly understood. Here, we investigated the role of PvRXLR111, a cell death‐inducing RXLR effector, in manipulating plant immunity. When coexpressed with other PvRXLR effectors, PvRXLR111‐induced cell death was prevented. Transient expression of PvRXLR111 in Nicotiana benthamiana suppressed bacterial flagellin peptide flg22‐elicited immune responses and enhanced Phytophthora capsici infection. PvRXLR111 induction in Arabidopsis increased susceptibility to Hyaloperonospora arabidopsidis. PvRXLR111 expression in Pseudomonas syringae promoted bacterial colonization. By immunoprecipitation‐mass spectrometry analysis, yeast two‐hybrid, pull‐down, and bimolecular fluorescence complementation assays, it was shown that PvRXLR111 interacted with Vitis vinifera putative WRKY transcription factor 40 (VvWRKY40), which increased VvWRKY40 stability. Transient expression of VvWRKY40 in N. benthamiana inhibited flg22‐induced reactive oxygen species burst and enhanced P. capsici infection and silencing NbWRKY40 attenuated P. capsici colonization. These results suggest VvWRKY40 functions as a negative regulator in plant immunity and that PvRXLR111 suppresses host immunity by stabilizing VvWRKY40.