*Club domestic league appearances and goals, correct as of 19:16, 2 May 2024 (UTC) ‡ National team caps and goals, correct as of 15:53, 27 January 2022 (UTC)
Martínez's career started with River Plate, initially featuring for their youth system; notably at the 2016 U-20 Copa Libertadores, though only as an unused substitute on three occasions.[1] He first appeared in River Plate's first-team under Marcelo Gallardo in October 2017, with the defender being chosen on the bench for an Argentine Primera División defeat away to Talleres.[1][4] His professional debut arrived on 2 December 2018 during a fixture with Gimnasia y Esgrima.[1]
In July 2019, Defensa y Justicia completed the loan signing of Martínez.[5] Across the next twelve months, the centre-back made twenty league appearances and scored two goals; against Godoy Cruz and Patronato.[1] He also made appearances in the Copa Argentina and Copa Libertadores.[1] Defensa extended his loan in April 2020, prior to signing him permanently in the succeeding August.[6][7][8]