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The intracellular pathogen Salmonella enterica serovar Typhimurium confronts cytoplasmic Mg2+ starvation inside macrophages. This stress alters carbon metabolism and subverts canonical carbon source preferences by reducing synthesis of 3′, 5′-cyclic adenosine monophosphate (cAMP), the essential allosteric activator of the cAMP receptor protein (CRP), master regulator of carbon utilization. How, then, does S. Typhimurium preferentially utilize CRP-cAMP-dependent carbon sources inside macrophages? We now report that the virulence and Mg2+ homeostasis regulator PhoP controls CRP-cAMP-dependent transcription, metabolism, and growth on a mixture of carbon sources during low cytoplasmic Mg2+. We determine that the PhoP-activated MgtA and MgtB proteins promote CRP-cAMP activity by importing Mg2+, indispensable cofactor of the cAMP-synthesizing adenylate cyclase CyaA. Significantly, the PhoP-activated MgtC preserves cAMP amounts despite reducing abundance of CyaA substrate adenosine triphosphate (ATP) because ATP at high concentrations inhibits CyaA. Restoring CRP activity by supplementation of cAMP or introduction of the constitutively active crp* allele corrected CRP-dependent transcriptional and growth behaviors of the mgtA mgtB mutant. By controlling cAMP synthesis, PhoP dictates the amounts of active CRP, thereby reprogramming S. Typhimurium’s metabolism.