ABSTRACT Diversion of the -containing vacuole (LCV) from the host endosomal-lysosomal degradation pathway is one of the main virulence features essential for manifestation of Legionnaires’ pneumonia. Many of the ∼350 Dot/Icm-injected effectors identified in have been shown to interfere with various host pathways and processes, but no effector has ever been identified to be indispensable for lysosomal evasion. While most single effector mutants of do not exhibit a defective phenotype within macrophages, we show that the MavE effector is essential for intracellular growth of in human monocyte-derived macrophages (hMDMs) and amoebae and for intrapulmonary proliferation in mice. The null mutant fails to remodel the LCV with endoplasmic reticulum (ER)-derived vesicles and is trafficked to the lysosomes where it is degraded, similar to formalin-killed bacteria. During infection of hMDMs, the MavE effector localizes to the poles of the LCV membrane. The crystal structure of MavE, resolved to 1.8 Å, reveals a C-terminal transmembrane helix, three copies of tyrosine-based sorting motifs, and an NPxY eukaryotic motif, which binds phosphotyrosine-binding domains present on signaling and adaptor eukaryotic proteins. Two point mutations within the NPxY motif result in attenuation of in both hMDMs and amoeba. The substitution defects of P and D are associated with failure of vacuoles harboring the mutant to be remodeled by the ER and results in fusion of the vacuole to the lysosomes leading to bacterial degradation. Therefore, the MavE effector of is indispensable for phagosome biogenesis and lysosomal evasion. Intracellular proliferation of within a vacuole in human alveolar macrophages is essential for manifestation of Legionnaires’ pneumonia. Intravacuolar growth of the pathogen is totally dependent on remodeling the -containing vacuole (LCV) by the ER and on its evasion of the endosomal-lysosomal degradation pathway. The pathogen has evolved to inject ∼350 protein effectors into the host cell where they modulate various host processes, but no effector has ever been identified to be indispensable for lysosomal evasion. We show that the MavE effector localizes to the poles of the LCV membrane and is essential for lysosomal evasion and intracellular growth of and for intrapulmonary proliferation in mice. The crystal structure of MavE shows an NPxY eukaryotic motif essential for ER-mediated remodeling and lysosomal evasion by the LCV. Therefore, the MavE effector of is indispensable for phagosome biogenesis and lysosomal evasion.