Born in Lodosa, Navarre, Martínez joined Real Sociedad from local CD Izarra, aged 13.

He played his first league match on 26 August 2007 in a 0–2 home loss against CD Castellón,[1] and scored his first goal on 25 November of that year to help the hosts beat Málaga CF 3–0.

[3] He made his debut in the competition on 29 August 2010 by featuring the full 90 minutes in a 1–0 home victory over Villarreal CF;[4] in the following seasons, he battled for first-choice status with fellow youth graduate Dani Estrada.

[5][6] In May 2018, after he made only a single Copa del Rey appearance since December 2016 due to injuries and the form of the emerging Álvaro Odriozola in his position,[7] the club announced that Martínez would be departing from the club on the expiry of his contract at the end of the campaign, at the same time as long-time teammate Xabi Prieto.

[10] On 9 August 2019, he moved down one tier and joined Burgos CF;[11] the following 15 January, he terminated his contract by mutual consent.