The RNA-binding protein Ataxin-2 binds to and stabilizes a number of mRNA sequences, including that of the transactive response DNA binding protein 43 kDa (TDP-43). Ataxin-2 is additionally involved in several processes requiring translation such as germline formation, long term habituation and circadian rhythm formation. However, it has yet to be unambiguously demonstrated that Ataxin-2 is actually involved in activating the translation of its target mRNAs. Here we provide direct evidence from a polysome profile analysis showing that Ataxin-2 enhances translation of target mRNAs. Our recently established method for transcriptional pulse-chase analysis under conditions of suppressing deadenylation revealed that Ataxin-2 promotes post-transcriptional polyadenylation of the target mRNAs. Furthermore, Ataxin-2 binds to a poly(A) binding protein PABPC1 and a noncanonical poly(A) polymerase PAPD4 via its intrinsically disordered region (906–1095 aa) to recruit PAPD4 to the targets. Posttranscriptional polyadenylation by Ataxin-2 explains not only how it activates translation but also stabilizes target mRNAs, including TDP-43 mRNA. Ataxin-2 is known to be a potent modifier of TDP-43 proteinopathies and to play a causative role in the neurodegenerative disease Spinocerebellar ataxia type 2, so these findings suggest that Ataxin-2-induced cytoplasmic polyadenylation and activation of translation might impact neurodegeneration (i.e., TDP-43 proteinopathies) and this process could be a therapeutic target for Ataxin-2-related neurodegenerative disorders.