He made his La Liga debut on 29 September in a 2–2 draw at Valencia CF and, during his 13-year spell with the club, would form an historic attacking partnership with Agustín Gaínza, José Luis Panizo and Telmo Zarra, helping Athletic to the 1942–43 league and four Copa del Generalísimo trophies.

After a couple of months, however, he returned to the top division and joined Real Sociedad, retiring shortly after the end of the 1954–55 season.

[5] In the 1968–69 campaign, Iriondo returned to Athletic Bilbao as head coach, helping the club to the 11th place in the league and the domestic cup.

Iriondo's last coaching job was with Real Betis: he led the Andalusians to the 1977 Spanish Cup,[6][7] but suffered top-flight relegation the following season.

[8] After 15 matches at Rayo Vallecano in 1980 (meeting the same fate) he returned to Betis for one final campaign in 1981–82, being one of three managers to help the team finish sixth in the top tier and qualify for the UEFA Cup for the first time ever;[9] he died in Bilbao on 24 February 2016, aged 97.