Orphaned at 11, Castle dropped out of high school at 15 to work in the theater. He came to the attention of Columbia Pictures for his talent for promotion, and was hired. He learned the trade of filmmaking and became a director, acquiring a reputation for the ability to churn out competent B-movies quickly and on budget. He eventually struck out on his own, producing and directing thrillers which, despite their low budgets, were effectively promoted with gimmicks, a trademark for which he is best known. He was also the producer for Rosemary's Baby.