To exercise its responsibilities effectively in the global interest, the legislative function in a reformed United Nations will require supporting advisory mechanisms for specialized scientific, technical and other expertise. Moreover, a strong civil society voice including nongovernmental organizations has been shown to contribute constructively to global policy-making; a Chamber of Civil Society could thus play a central advisory role to the General Assembly. The goal will be to ensure an effective UN decision-making capacity, based on the best available knowledge and analysis, to address global challenges. Additional supporting mechanisms are necessary to support this process; advisory bodies made up of individuals with established expertise would initially focus their efforts on several pressing global catastrophic risks, including climate change, the deterioration of the environment, nuclear proliferation and the peace and security challenges this raises. An excellent precedent in this area is the Intergovernmental Panel on Climate Change (IPCC). In the scientific domain beyond pressing global catastrophic risks, the General Assembly will need to have a number of general advisory mechanisms to provide additional specialized expertise, supplemented by an ethical advisory process in an Office of Ethical Assessment, to provide analysis of the ethical implications of issues under consideration.