Combative and with good passing skills, he spent the vast majority of his professional career with Athletic Bilbao, appearing in 510 competitive games during 12 seasons.
Iraola was born in Usurbil, Gipuzkoa. A product of Athletic Bilbao's youth system at Lezama after joining from Antiguoko, he made his debuts with the first team in the 2003–04 season, becoming an instant first-choice while often taking penalties and free kicks. On 30 August 2003 he made his first La Liga appearance, starting in a 0–1 home loss against FC Barcelona, and his five goals in 30 appearances helped the team qualify for the UEFA Cup.
During his twelve seasons Iraola never played in fewer than 30 league matches, scoring in all but one league campaign – like former club legend Aitor Larrazábal, who played as a left back– while also helping the Basque side finish second in three Copa del Rey tournaments and the 2011–12 UEFA Europa League. On 28 January 2007 he netted twice in a 2–0 away win against neighbours Real Sociedad, who were finally relegated – Athletic narrowly avoided the drop, ranking in 17th position. He played his first cup final in 2009, a 1–4 loss to Barcelona at Mestalla in Valencia, and three years later helped them finish runners-up in both the domestic cup and the Europa League.
2012–13 marked the first year where Iraola failed to find the net in the league, but he continued to be the side's automatic first-choice in his position as he featured in 35 games. His only goal of the season came on 24 August 2012 in a 6–0 home routing of HJK Helsinki for the playoff round of the UEFA Europa League (9–3 on aggregate).
On 4 December 2013, Iraola renewed his contract with the club, keeping him at the San Mamés until 30 June 2015. He captained the team in his last match, the 2015 Copa del Rey Final which was lost 1–3 to Barcelona; in the 24th minute of his last league appearance, the previous weekend against Villarreal CF, Aritz Aduriz offered him the taking of a penalty kick but he declined, so the former converted it instead.
On 16 June 2015, aged 33, Iraola moved abroad for the first time in his career, signing for Major League Soccer club New York City FC. He made his debut against Toronto FC at the Yankee Stadium on 12 July, playing the entirety of a 4–4 draw.
On 17 November 2016, Iraola announced his retirement.
On 20 August 2008, Iraola was called by new Spain coach Vicente del Bosque for a friendly with Denmark, alongside teammate Fernando Amorebieta. He entered the pitch in the final 15 minutes of the 3–0 away success, coming in as a substitute for Sergio Ramos.
On 29 March 2011, after nearly one-and-a-half years without playing for the national team, Iraola started in a 3–1 win against Lithuania in Kaunas for the UEFA Euro 2012 qualifiers. He was due to make the cut for the final squad, but injury forced him out in favor of Atlético Madrid's Juanfran.Athletic Bilbao
UEFA Europa League: Runner-up 2011–12
Copa del Rey: Runner-up 2008–09, 2011–12, 2014–15
Supercopa de España: Runner-up 2009