Castro Medellín was born in Mineral de La Noria, Sombrerete, Zacatecas, Mexico, in the Archdiocese of Durango, on 21 June 1938, the third of five children.
In 1971 after two years of study he earned a licentiate in moral theology at the Alphonsian Academy in Rome.
From 1992 to 2002 he was vicar for religious and consecrated life in the diocese of Zamora, serving also from 1997 to 2002 as pastor of the Sagrada Familia parish in Uruapan.
[1] On 25 October 2002, Pope John Paul II named him bishop of Tacámbaro.
[1] He received his episcopal consecration on 3 December[2] from Archbishop Giuseppe Bertello, Apostolic Nuncio to Mexico.