Simeon Marcelo graduated in 1979 among the top of his law class from the University of the Philippines and placed no. 5 in the bar examinations. With top corporations and then president Ramos as clients, he had distinguished himself as a top-notch litigator after twenty years of private practice of law. He caught national public attention during the nationwide live televised 2000 impeachment proceedings against then president Estrada, having been selected to present the prosecution’s star witness. 

In February 2001, he was appointed as solicitor general. His focus on the Marcoses and their cronies resulted in the recovery of PHP130 billion ill-gotten wealth (compared to the PHP26 billion recovered since the 1986 revolution). Having won all of his major cases, Marcelo was appointed as the youngest head of the country’s anti-corruption body in 2002. As ombudsman, he led the prosecution team that secured the historical first ever plunder charge conviction of a former president.

Having returned to private practice in January 2008, he was engaged as counsel of the biggest local power utility, thwarting successfully a hostile take-over. The central bank tapped him to prosecute the persons responsible for the biggest bank fraud case in the country’s history. A leading company engaged him in a multi-billion tax collection suit. In 2014, he secured from the Supreme Court a decision, annulling a tax assessment of his client’s aviation fuel sales to international carriers, which was costing it PHP100 million annually. He led his team in winning another multi-billion tax case in the Supreme Court in 2018.

In 2013-2014, he served with an ICC Tribunal that handled two related disputes. The following year, he headed the panel that secured a favorable award in an important construction arbitration dispute. Subsequently, he became the chairman of the tribunal that handled a very significant international arbitration case.

From December 2008 to June 2014, he served as one of the four members of the World Bank’s independent advisory board. In June 2013, he was conferred by the University of the Philippines Alumni Association (UPAA) the distinguished alumni award in public service. Currently, he serves as legal counsel in high-profile cases in various courts, including the Supreme Court.