Martínez was born on January 18, 1998 in Gualeguay, Argentina. The defender came over from Argentina's Defensa y Justicia in 2019.
On July 27, 2019, he made his debut in the first team during the Ajax – PSV (2-0) match for the Johan Cruijff Shield. He has so far played 91 official matches in Ajax's first team and scored five goals.