We previously reported that manganese (Mn) enhances innate immune responses to viral infection by inducing phosphorylation of TANK-binding kinase 1 (TBK1) in an Ataxia-telangiectasia mutated (ATM)-dependent manner. However, the underlying mechanism by which how Mn induces TBK1 phosphorylation remained unclear. Here, we show that Mn dose-dependently induced TBK1 phosphorylation in the presence of ATM across multiple cell lines, as well as in primary human macrophages and T cells. This phosphorylation was abolished in ATM-deficient cells, and we identified cytoplasmic ATM as a key mediator. Immunoprecipitation assays revealed that Mn promoted ATM phosphorylation at Ser1893, Ser1981, and Ser2996. TBK1 interacted with phosphorylated ATM at early stages, but upon phosphorylation, TBK1 dissociated from the ATM-TBK1 complex. This dissociation coincided with enhanced antiviral cytokine production. Furthermore, Mn dose-dependently suppressed HIV replication by inducing multiple antiviral host factors and cytokines. Together, these findings identify a cytoplasmic ATM-TBK1 phosphorylation cycle as a critical regulator of antiviral innate immunity and suggest Mn supplementation as a potential therapeutic approach against HIV and other viral infections.