Martínez's first major win came at the 1999 Summer Universiade, where he became the champion in the 10,000 metres. He competed at the 2001 World Championships in Athletics, finishing 13th in the final, but was more successful at the European Athletics Championships, in which he won the 2002 gold medal in the 10,000 m, and returned to take the silver medal at the following edition in 2006. He won the San Silvestre Vallecana 10K race in Madrid in 2003.