Upon being admitted to the bar that same year, Negrón García went to work as a legal advisor for the Puerto Rico Power and Water company.
From 1972 to 1974 he presided over the Governor's Judicial Appointment Advisory Committee, as well as serving as Executive Secretary of the Justice Reform Council of Puerto Rico.
After Trías Monge's appointment to Chief Justice in 1974, there remained one vacancy in the Supreme Court.
Governor Rafael Hernández Colón had avoided filling the spot until Negrón García had fulfilled the Supreme Courts requirement for membership: ten years as a licensed jurist in Puerto Rico.
He writes occasional columns for El Nuevo Día, and he serves as an advisor to the Joint Commission on the Revision of the Civil Code of Puerto Rico in the matter of torts.