Medellín, Colombia, managed to turn itself from one of the most violent and unequal places in the world to a more safe, inclusive and healthy city. Medellín is recognized for this transformation and its innovative city planning, design and development. This paper highlights some of the key drivers behind Medellín's transformation and the lessons these factors have for other cities seeking to reduce inequality and violence. We combine one-on-one interviews with key stakeholders involved in Medellín's transformation, with reviews of archival documents, media content analyses and ideas revealed during a six-month seminar on the transformation of Medellín held at the University of California, Berkeley, in 2017. We suggest that a set of inter-related factors, from civil society mobilization, to urban governance reforms to public space investments in the poorest neighborhoods, combined to help transform Medellín's built, social, natural, political and economic environments. While the transformation of Medellín may be ongoing and incomplete, we suggest that the factors analyzed here offer insights for planning more healthy and equitable cities globally.