Justice De Castro was appointed to the Supreme Court on December 4, 2007.  She is an alumna of the University of the Philippines (UP) where she was a consistent college and university scholar. She finished in UP, Bachelor of Arts cum laude in 1968 and Bachelor of Law in 1972 at the top four of her class.  She was Vice-Chancellor and a consistent member of the UP College of Law honor society, the Order of the Purple Feather. She was elected to lifetime membership in the Phi Kappa Phi International Honor Society and Pi Gamma Mu International Honor Society in the Social Sciences for academic excellence in her Bachelor of Arts and Bachelor of Laws degrees. She attended law courses in the International Law Institute in Washington D.C., USA and Harvard Law School’s Program of Instruction for Lawyers in Massachusetts, USA.

Now on her 39th year in government, Justice De Castro’s career in public service began on February 19, 1973, when she was appointed to a law clerk position in the Office of the Clerk of Court of the Supreme Court. From January 1975 to November 1978, she served as a Legal/Judicial Assistant and as member of the technical staff of the late Chief Justice Fred Ruiz Castro. In December 1978, she transferred to the Department of Justice (DOJ) where she served as State Counsel I and rose from the ranks culminating in her appointment in 1997 as Assistant Chief State Counsel. She was designated as one of the international and peace negotiators of President Corazon Cojuangco Aquino and President Fidel V. Ramos from 1988 to 1997. In 1998, she was awarded by then President Fidel V. Ramos with the Presidential Medal of Merit for Exceptionally Meritorious and Valuable Service Rendered and Remarkable Accomplishments that have served the interest of peace, unity and progress in Southern Philippines, earning her the gratitude and admiration of the Filipino nation and the people.

Justice De Castro rejoined the Judiciary as Sandiganbayan Associate Justice on September 23, 1997 and became its Presiding Justice on December 15, 2004. During her incumbency, she spearheaded the establishment of the Computerized Case Management System and the adoption of reforms that contributed to easing of the court docket in the Sandiganbayan and to the professionalization of its work force. For these accomplishments as Presiding Justice of the Sandiganbayan, she was awarded in December 2005 the Chief Justice Hilario G. Davide Judicial Reform Award.

She now holds the position of President-elect, for the term 2012-2014, of the International Association of Women Judges (IAWJ) pursuant to her election in May 2012 at the Biennial Convention of the IAWJ held in London, United Kingdom, which was attended by members of the Chapters of the IAWJ from over 100 countries. She is also currently the President of the Philippine Women Judges Association (PWJA).

In the Supreme Court, Justice De Castro is the Working Chairperson of the First Division, the Chairperson of the Management Committee of the Judicial Reform Support Project, the Working Vice-Chairperson of the Committee on Ethics and Ethical Standards and of the Halls of Justice Coordinating Committee, Chairperson of the Committee on Computerization and Library, the Committee on Gender Responsiveness in the Judiciary, and the Special Committee to Draft Rules on Sexual Harassment in the Judiciary, and Member of the Supreme Court Internal Rules Committee.