Before her Sandiganbayan appointment, De Castro was State Counsel V and Legal Staff head at the DOJ (1989–1995).

[9] De Castro was the Presiding Justice and Chair of the First Division, Sandiganbayan at the time of her appointment to the High Court.

[14] De Castro headed the anti-graft court's special division on the perjury and plunder trial of former President Joseph Estrada.

[18] She vigorously denied those rumors, claiming that she had been a candidate for a seat on the high court before her involvement in the case.

On October 16, 2007, the Judicial and Bar Council (JBC) announced the final nominees to the Associate Justice Cancio Garcia's vacant seat.

We are convinced, then and now, that the special court created to exclusively try the case of President Estrada was established precisely to convict him, which is what exactly happened.

[citation needed] De Castro was one of five sitting justices who sought to nullify the appointment of Maria Lourdes Sereno as the country's top magistrate.

De Castro and Sereno were both shortlisted by the Judicial and Bar Council in 2012 for the Chief Justiceship but then-President Benigno Aquino III appointed the latter to the post.

On August 25, 2018, De Castro was appointed by President Rodrigo Duterte as the Chief Justice of the Supreme Court, following the ouster of Maria Lourdes Sereno via quo warranto.