 Starting out as a private practitioner, he then worked at the Office of the Solicitor General, from which he was subsequently appointed as a judge, then a Court of Appeals Justice before being appointed as Supreme Court Associate Justice in 1954.Concepción, one of the leaders of the Civil Liberties Union and a Constitutional expert in his own right, advocated the promotion and protection of civil and individual liberties.His dedication to the Rule of Law was his hallmark.