This research aims to identify and analyze the critical success factors (CSF) of information technology outsourcing (ITO) in a Brazilian municipal public agency. The success factors of ITO were identified through a systematic literature view, which retrieved 314 articles from the ACM and IEEE databases, 30 of which met the research protocol criteria. The Delphi technique was used as a research method to determine the CSF based on the success factors identified in the literature. The Delphi panel included thirty-five experts, and the data were collected in 2018. The results indicate the existence of six CSF information technology outsourcing: Communication, Technical Ability, Commitment, Conformity, Context and Confidence. The survey also identified that the processes of implementation, and the behavior between the client and the supplier, play a more critical role in the success of the ITO than hiring processes. The research suggests that contractual clauses, while important, are not sufficient to guarantee the success of ITO initiatives. Moreover, theories with a social perspective contribute more than economic theories when it comes to analyzing ITO in public agencies.