On 9 April 2017, while still a junior, Ruiz made his senior debut with the reserves, coming on as a late substitute for Jesús Alfaro in a 2–0 Segunda División B away win against Badalona; he also became the first player born in the 2000s to make an appearance for the club's senior ranks.[5]
After Barcelona B's promotion, Ruiz made his professional team debut on 28 August 2017, replacing David Concha in an 3–0 home loss against Tenerife in the Segunda División championship.[6] Four days later he scored his first professional goal in a 2–2 draw against Granada.[7]
On 31 January 2020, Ruiz joined Portugal's Braga on loan for the rest of the season, with a mandatory purchase for €8 million and a buy-back clause.[10] He made his debut on 20 February in the round of 32 first leg of the UEFA Europa League away to Rangers, starting the game and scoring in a 3–2 loss.[11] Totalling eight appearances over the season, he scored his first Primeira Liga goal on 4 July soon after entering in a 4–0 home win over Aves.[12]
Ruiz was the top scorer in the Taça de Portugal as Braga won it in 2020–21, contributing seven goals in as many games.[13] This included two in a 3–2 win away to Porto in the semi-finals.[14]
In 2021–22, Ruiz scored in each leg of a 3–1 aggregate win over Monaco in the Europa League last 16.[15] He netted the only goal of the game in the next fixture against Rangers, though the Scots won 3–2 over the two games after extra time.[16]
Girona
On 27 June 2024, Ruiz signed for La Liga club Girona on a contract until June 2029.[17]
Ruiz finished the competition with four goals, being awarded the Silver Boot; he was also included in the tournament's best eleven.[20] During the 2017 edition in Croatia, he captained the side as Spain achieved their ninth title.[21]
On 22 September 2017, Ruiz was included in Santiago Denia's squad ahead of the 2017 FIFA U-17 World Cup,[22] and scored two braces in the tournament, scoring two goals in a 4–0 win against Niger on 10 October, and two more in a 3–1 semi-finals win against Mali on 25 October.[23]
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.[24] Ruiz made his senior debut in the 4–0 win in Leganés, missing a penalty in the match.[25][26]
At the 2023 UEFA European Under-21 Championship, in the 20th second of the match against Croatia, Ruiz scored the quickest goal in the history of the tournament, bringing a 1–0 victory to Spain and advancement to the quarter-finals.[27]