Martínez made his senior debut on 20 August 2017, starting in a 1–1 home draw against Melilla.[3] He finished the campaign as a starter, as his side avoided relegation.
Martínez made his first team debut on 28 April 2019, playing the full 90 minutes of a 4–1 home routing of Lugo in the Segunda División championship.[4] On 17 June, he was definitely promoted to the main squad.[5]
RB Leipzig
On 22 January 2020, RB Leipzig reached an agreement with Las Palmas for the transfer of Martínez, effective as of 1 July.[6] He agreed to a contract until 2024 with his new club.[7]
Genoa
On 29 June 2022, Martínez was loaned to Genoa in Italy for the Serie B 2022–23 season.[8]
On 9 June 2023, since the inclusion of a "sell-out" right following the promotion to Serie A, Martínez was bought by Genoa.[9]
Inter Milan
On 9 July 2024, Martínez signed for fellow Serie A side Inter Milan on a permanent basis.[10]
International career
Due to the isolation of some national team players following the positive COVID-19 test of Sergio Busquets, Spain's under-21 squad were called up for the international friendly against Lithuania on 8 June 2021.[11] Martínez made his senior debut in the match.[12]