Martínez was born on 17 October 1995 in the municipality of Melchor de Mencos in Petén Department, but grew up in San Benito. He began boxing at the age of twelve and won the schoolboy national championship in 2009. He soon moved to the capital, Guatemala City, to continue his development. He won his first international competition in 2011, earning a gold medal at that year's Central American Championships in Managua. The following year, he repeated as Central American champion and won gold at the Panamerican School Games before taking home a silver at the Youth World Championships in Yerevan, becoming the first Guatemalan to ever medal at an AIBA world championship. He also lost to Jamel Herring in the 2012 American Boxing Olympic Qualification Tournament. After achieving back-to-back first-place finishes at the Central American Games in 2013 and 2017, he became the first Guatemalan boxer in 68 years to win gold at the Central American and Caribbean Games when he beat former World and Olympic champion Arlen López for the middleweight crown in 2018.