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The bacterial pathogen Legionella pneumophila exploits host cell vesicle transport by transiently manipulating the activity of the small guanosine triphosphatase (GTPase) Rab1. The effector protein SidM recruits Rab1 to the Legionella-containing vacuole (LCV), where it activates Rab1 and then AMPylates it by covalently adding adenosine monophosphate (AMP). L. pneumophila GTPase-activating protein LepB inactivates Rab1 before its removal from LCVs. Because LepB cannot bind AMPylated Rab1, the molecular events leading to Rab1 inactivation are unknown. We found that the effector protein SidD from L. pneumophila catalyzed AMP release from Rab1, generating de-AMPylated Rab1 accessible for inactivation by LepB. L. pneumophila mutants lacking SidD were defective for Rab1 removal from LCVs, identifying SidD as the missing link connecting the processes of early Rab1 accumulation and subsequent Rab1 removal during infection.