After initiating his career with Independiente Medellin in 2004 and becoming the league's top scorer in 2009, he attracted interest from Chiapas, who signed him in January 2010. He spent three years with the Mexican side before moving to Portugal to play for Porto, where he was Primeira Liga's top scorer in all three of his seasons with the club. In July 2015, Martínez joined Atlético Madrid for €35 million, and six months later Guangzhou Evergrande of China for €42 million. He unfortunately suffered an ankle injury in late 2016 that ruled him out for two years, before ending his career back in Portugal with Portimonense in 2020.