The European Parliament (EP) maintains relations with almost all third countries in the world, including the European Union (EU) strategic partners, such as Mexico. However, the EP’s influence on EU external relations remains unclear in the literature, especially when acting as a guardian of human rights. Based on three major case studies of human rights abuse in Mexico: the Chiapas conflict, feminicide and the disappearance of the 43 students from the Ayotzinapa Rural Teachers’ College, the chapter inquires whether the EP has influenced EU relations towards strategic partners while fulfilling its role of promoting human rights worldwide, and if so, how EP delegations and civil society organisations (CSOs) have contributed to this influence. The chapter provides an in-depth understanding of the performance of the EP, its parliamentary delegations and CSOs over time (1995-2016) and before and after the establishment of the EU-Mexico strategic partnership, as well as interesting insights for parliamentary diplomacy in general drawn from pioneering empirical research. The chapter concludes that the EP has exerted influence on EU relations towards strategic partners. Its delegations and CSOs have indeed contributed to this influence through different means, such as information provision and joint advocacy.