As a human rights lawyer, he had:

• Argued before the Supreme Court of the Philippines in support of minorities, the Party List Election Case in 2000, which led to the Supreme Court ordering that 20 per cent of the seats in Congress be reserved for the marginalised and underrepresented poorer citizens,
• Played a central role in bringing about constitutional change following the infamous Pork Barrel Case, a political scandal in which public funds allocated for development projects in the Philippines were being misused by several members of Congress;
• Helped organise the Counsels for the Defence against Attacks on Lawyers, a group of lawyers and law students advocating against the unlawful killings and arrests of their colleagues under then President Gloria Arroyo (2005),
• Been elected founding Secretary General of the National Union of People’s Lawyers, a group of lawyers providing legal aid to the victims of human rights violations (2007),
• Established Manlaban sa EJK alongside fellow human rights lawyers, constitutionalists and several law students (2017),
• Counseled in a complaint against President Duterte for crimes against humanity, filed to the International Criminal Court (ICC) by families of extrajudicial killing victims;
• Been one of the prosecutors in handling high-profile cases such as the impeachment cases of Renato Corona, Ombudsman Merci Gutierrez, and President Gloria Arroyo, constitutionality of Executive Order 464, Emergency Rule Proclamation 1017, and the Visiting Forces Agreement in the light of the Subic Rape Case