Castillo earned both his undergraduate and masteral degrees from De La Salle University in Manila. Before entering politics, he served different positions in financing companies, and worked as a Special Assistant to then Cavite Governor Juanito Remulla. In 1992, he ran for congressman under the Remulla ticket but lost; then in 1995 he vied for the mayorship of Bacoor but got the same result, being defeated by the late Victor Miranda. However, just four months before the 1998 elections, he was declared the duly-elected mayor after the court upheld his complaint of vote-rigging. He again ran for mayor in 1998 and won, and he would serve for three terms.