He made his senior international debut in 2021 and was included in the squad for the 2021 UEFA Nations League Finals in Italy, in which Spain finished as runners-up.

[6] On 28 November 2017, before even appearing with the reserves, Porro made his first team debut by coming on as a late substitute for goalscorer Johan Mojica in a 1–1 away draw against Levante, for the season's Copa del Rey.

Porro made his La Liga debut on 17 August 2018, starting as right back in a 0–0 home draw against Real Valladolid.

[11] Porro established himself as a starter under Eusebio Sacristán, becoming first choice ahead of Aday Benítez and replacing departed Pablo Maffeo.

[18] On 24 September 2020, he made his debut for the club in a 1–0 home win against Aberdeen in the third qualifying round of the UEFA Europa League.

[19] After arriving in Lisbon at the Estádio José Alvalade under some suspicion for young age, Porro immediately established himself as starter in the right side of the defence, making his league debut in a 2–0 away win against Paços de Ferreira.

[28] On 24 November, Porro scored the third goal against Borussia Dortmund in a 3–1 home win at a group stage match of the 2021–22 UEFA Champions League, by converting the rebound after Gregor Kobel saved a penalty from Pedro Gonçalves, to ensure his team qualification to the round of sixteen, for the first time since the 2008–09 season.

[30] He made his return from injury on 29 January 2022, with his crucial assist to Pablo Sarabia helping his team come from behind to defeat crosstown rivals Benfica 2–1 in the 2021–22 Taça da Liga final.

[40] In March 2021, Porro received his first call-up to the Spain national football team for the group stage of the 2022 FIFA World Cup qualification.