This article analyze the process by which human rights expertise in Argentina gained a critical place on the public agenda and State policies from the beginning of democracy. For doing so, I'll study the social trajectories of several groups of legal professionals who promoted and made possible that human rights gained an important place. This analysis shows the value of the important confluence of the legitimacy acquired by this legal expertise since the inclusion of Argentine lawyers in transnational networks, the professionalization of human rights activism and the participation of some of its leaders in key positions within the state structure. The import of this form of expertise produced transformations in the State and in the ways of understanding the commitment to public causes. Through an extensive process to be described here, a new legal and political elite was produced in Argentina.