Agustín Eizaguirre was born in the Basque Country and was a one-club man as he played only for Real Sociedad from 1912-25. He played more than 60 matches as goalkeeper for his club including one Copa del Rey (Spanish Cup) final. In 1913 he played in the last two of the three finals against FC Barcelona in the UECF (Unión Española de Clubes de Fútbol) Copa del Rey, but Real Sociedad lost the third match after two draws. This competition was played simultaneously with the cup organized by the Spanish Football Federation, nevertheless both competitions are official today. He never played for the Spanish national team, but his son Ignacio earned 18 caps for Spain as goalkeeper.