A youth product of Osasuna, he spent three seasons in La Liga before switching to Marseille, winning four major honours with the French club. In the summer of 2012 he moved to Chelsea, winning the Europa League in his first season and a domestic double two years later.
Azpilicueta earned 55 caps for Spain at youth level in all age groups, and represented the under-21s in two European Championships, winning the 2011 edition. He made his first appearance with the full side in 2013, and was selected for the 2014 World Cup and Euro 2016.
Azpilicueta was born in Pamplona, Navarre. A product of hometown club CA Osasuna's youth system, he made his La Liga debut on 8 April 2007 in a 0–2 away loss against Real Madrid, while still registered with the reserve team; he started his career as a forward then switched to midfielder and, throughout both his club and international career (senior and youth), appeared in several positions including central defender and central midfielder.
In 2007–08, due to injuries in the main squad, Azpilicueta established himself as a first-team regular at the age of just 18, albeit as a right-back. He went on to retain this position for the following season, appearing in all but two league games.
On 21 June 2010, French club Olympique de Marseille confirmed an agreement had been reached with Osasuna for the transfer of Azpilicueta, in a four-year contract for €7 million. A week later, the Navarrese confirmed the agreement, with the transfer fee possibly rising to as much as €9.5 million depending on appearances. In his UEFA Champions League debut he scored the match's only goal in a group stage home match against FC Spartak Moscow, albeit in his own net.