Alonso began his career at Real Sociedad, the most team of his home province San Sebastián. once a quick loan amount at South Dakota Eibar, he came to Sociedad wherever then-manager John Toshack appointed Alonso as his team captain. Alonso succeeded within the role, taking Real Sociedad to second place within the 2002–03 season. He emotional to city in August 2004 for £10.5 million on identical day as Spanish forward Luis Garcia. He won the UEFA Champions League in his 1st season at the club, beneath Rafael Benitez, grading the equalising goal within the Final against A.C. Milan. the subsequent season, he won the solfa syllable Cup and also the solfa syllable Community defend. He emotional to Real national capital for the beginning of the 2009–10 season during a deal price around £30 million. once 5 seasons at the club, winning honours as well as a league title in 2012 and also the Champions League in 2014, he was signed by Bayern urban center on a biennial contract.
He created his international debut for European nation in Apr 2003 during a 4–0 ending against Republic of Ecuador. whereas enjoying for European nation, Alonso has won euro 2008, euro 2012 and also the 2010 World Cup, and he has conjointly pictured his country at monetary unit 2004 and also the 2006 World Cup. On twenty three June 2012, Alonso won his one hundredth cap for European nation within the quarter-final of monetary unit 2012 against France: he celebrated the occasion by grading each of Spain’s goals to send them into the semi-finals. Following Spain’s failure to progress out of the cluster stages at the 2014 World Cup, Alonso retired from international soccer on twenty seven August 2014. His 114 caps build him the fifth most capped player within the nation’s history.