The applicability of Lean practices has been growing in the most different types of organizations, including public ones. Considering the growing need for better and more effective management systems, the objective of this work is to evaluate the influence of Lean practices on process effectiveness. A literature review was carried out to find Lean practices applicable to the public sector organizations and to outline the hypotheses of the work. The method of work consists of a survey, whose data collection was conducted through a questionnaire. The population of the study was composed by all the administrative servants of a public institution in Brazil. A valid sample of 997 answers was obtained from the studied institution. The data analysis was carried out by means of descriptive statistics, exploratory and confirmatory factor analysis, and multiple regression. The results allow identifying a positive influence of four Lean practices on the effectiveness of processes, which are: “Continuous improvement,” “Long-term thinking,” “Leadership support,” and “Focus on the final user.” The results also showed the influence of some dummy variables, such as “time in the public service” and “being head of sector.” As a conclusion of this work, it can be stated that Lean practices act as a basis for the effectiveness of processes and may optimize operational and administrative activities in public organizations.