Although initially a football player in his youth, Díaz-Miguel's physical characteristics, including a 1.86 m (6'1 1 1⁄4")[1] barefoot height, and also his determination, contributed to his start in basketball, as a player, at the Instituto Ramiro de Maeztu Secondary School of Madrid, where the Estudiantes ("students") club was founded in 1950, with pupils and teachers of the school.

He won the top-tier level Spanish Clubs League championship twice, in 1960 and 1961, with Real Madrid.

Díaz-Miguel had 27 caps as a player of the senior Spain national basketball team.

Immediately after his retirement from his basketball playing career, Díaz-Miguel started coaching Águilas Bilbao.

He was the head coach of the senior Spain national basketball team, for as long as 27 years (1965–1992).