In fact, the precept of responsibility to protect commonly termed as R2P has been developed for early response to prevent mass atrocity crimes, e.g. genocide, war crimes, ethnic cleansing or crimes against humanity. The central focus of responsibility to protect (R2P) on the protection of atrocity victims, theoretically, legalize the external intervention in internal affairs. Unfortunately, in case of application the precept faces some challenges which undermine the universal acceptance of R2P as a tool of humanitarian assistance. In addition to, international response in domestic affairs is a controversial issue in context of absolute state sovereignty. In this context, the study is undertaken to identify the legality of R2P to prevent mass atrocities in international law and the challenges of R2P. The study finds that lack of collaboration among the concerned international institutions, lack of collective conscience of international leaders and resource scarcity have been significant challenges to the norms of R2P doctrine. The study culminates that political will might implement the doctrine properly. To this effect, diversity of regional and international political character and the ambivalent attitude of individual states to overseas conflict should be minimized. Doctrinal research method is followed in the present study.