In the classical system of international law, states have largely used religion as an instrument in their reciprocal relations. This “instrumental” interpretation of religion was often a reason of conflict rather the ground of religious freedom. Since its origins, yet, the international legal system has changed and it is reasonable to ask what role religion plays at present day in international relations. The present article aims at suggesting that religion – or more exactly “religiosity” – can be an element of diplomacy. Taking the transformation from International to “global law” into account, this article promotes a constructive, not-more instrumental, role of religion, useful to prevent the States from the use of force. In so doing, it offers some insights into the differences between “religion” and “religiosity” in the contemporary human rights’ discourse; analyzes the recent involvement of religious leaders in global law; presents the emergence of a new methodology, called “Religious Diplomacy”. This methodology is supported by the increased number of international provisions encouraging a major engagement of religious actors into diplomacy. As a result, international community could enhance human religiosity as a factor of diplomacy. International organizations such as United Nations, Organization for Security and Cooperation in Europe, and European Union should use their convening power to initiate new, multi-layered frameworks of engagement, inclusive of the representatives of global religions. This could make multilateralism more fit for purpose and have a major impact over time on the global peaceful relations among states and international actors.