In 1990, Castillo joined Atlético Marte of El Salvador, he then moved to Costa Rica to play with Herediano.
In August 2000, Castillo signed as new coach of Municipal Limeño of El Salvador, replacing Rubén Alonso.
In December 2008, he signed as coach of Luis Ángel Firpo, replacing Óscar Emigdio Benítez.
He then accepted to coach Suchitepéquez of Guatemala, and helped the small club reach the semi-finals of the Clausura 2010.
On December 17, 2012, he was announced as new manager to El Salvador, replacing Juan de Dios Castillo.
In May 2016, Castillo signed as new coach of Sonsonate for the Apertura 2016, replacing Ennio Mendoza and Mario Elias Guevara.
In December 2018, Isidro Metapán reached the quarter-finals of the Apertura 2018, but they were defeated by FAS 0–2 on aggregate.