Modernization of Public Administration (PA), to provide a high-quality service, requires improvements in managerial personnel assessment processes. For this purpose, we developed and validated a management competency model that would enable Spanish PA to enhance organizational achievements and prevent corrupt practices. Relations between managers’ competencies and their performance would be perceived as a fairer assessment of human resources processes and ultimately lead to the promotion of ethical behavior within the organization. We followed a mixed-method approach. Study 1 began with a content analysis of articles referring to managerial competencies, followed by Focus Groups and a Delphi panel procedure with subject matter experts, which resulted in a model of eight competencies. Based on this model, in Study 2, we developed a reliable and invariant-across-gender questionnaire (Public Manager Competencies Questionnaire – PUMACQ), which was validated with composite performance criteria (task, contextual, and unethical pro-organizational behavior), by means of a cross-sectional design survey on public managers from around Spain ( N = 439), using structural equation analyses. Our main results show significant relationships between job performance and the competencies of leadership, communication, engagement with PA, innovation orientation, and ethics. Finally, we discuss the practical applications of the results in the public context.