The firm was founded in 1981 by a group of lawyers with the vision of establishing a highly professional, dynamic, and full service legal practice. Originally named Castillo Laman Tan and Pantaleon, the firm was formed with seventeen (17) lawyers.

Gregorio R. Castillo (Founding partner 1981-1992,deceased), Noel A. Laman, Ancheta K. Tan and Polo S. Pantaleon, the name and founding partners, were former partners of a major Philippine law firm.

In 1995, Roberto V. San Jose, a distinguished corporate law practitioner, joined the firm. Since then, the firm has been renamed Castillo Laman Tan Pantaleon & San Jose.

Today, the firm has a total of 48 lawyers and four legal assistants, a number consistent with its growth philosophy of judicious expansion. It has a support staff consisting of 13 paralegals and a full complement of administrative and accounting personnel, inclusive of a management information system team.