Non-governmental organizations (NGOs) are prominent actors in international human rights advocacy. While their access to intergovernmental organizations (IGOs) has increased over time, it is not clear why international institutions provide opportunities for NGOs and even encourage NGOs to cooperate with one another in pursuit of improvements in human rights. This dissertation investigates the consequences of NGO cooperation on government behaviors at United Nations human rights mechanisms. I compile original data and employ both quantitative and qualitative approaches to reveal the impact of NGO cooperation during human rights reviews on both third-party and targeted governments. The dissertation shows third-party governments are more likely to pressure peers to improve human rights in areas that NGOs have cooperatively identified for action. Targeted governments are also more likely to comply with the peer recommendations they accept when NGOs have cooperated. Yet, targeted governments are less likely to accept recommendations for improvement in their human rights when they receive more powerful pressure due to NGO coalitions. Supplementary qualitative evidence illustrates that NGOs strategically choose joint reports to better influence governments. This dissertation suggests that IGOs can design ways to harness NGO influence at international institutions to achieve shared goals, such as human rights promotion.