The Law School began operating only in 1936 and Claudio belonged only to the second batch of Ateneo Law School graduates. Claudio became the first ever Ateneo  bar topnotcher in 1940, starting a tradition that continues to this day, having topped the exam with an average of 94.35%.

He practiced law with great statesmen as Claro M. Recto, Jose W. Diokno, and eventually partnered with Senator Lorenzo Tanada and Emmanuel Pelaez. Appointed undersecretary and later secretary of the Department of Justice by President Ferdinand Marcos, he instituted reforms in the criminal justice system, notably dedicated circuit criminal courts to increase the speed of criminal trials.

He was appointed associate justice of the Supreme Court on April 19, 1979 and he is still best remembered today for his erudite pen and high integrity. Later during the period of martial law, his decisions and dissenting opinions cast doubt on the validity and legality of the martial law regime. During the ratification process of the 1973 Constitution, Justice Teehankee spoke consistently that the Constitution must remain superior. In his words, “This is so because the Constitution is ‘superior paramount law, unchangeable by ordinary means’ but only by the particular mode and manner prescribed therein by the people. As stressed by Cooley, by the Constitution which they establish, (the people) not only tie up the hands of their official agencies but their own hands as well; and neither the officers of the State, nor the whole people as an aggregate body, are at liberty to take action in opposition to this fundamental law.

During the proposed 1976 amendments to the Constitution wherein President Marcos would continue office not by reason of popular elections, but by referendum, and to serve as prime minister during the process of reorganization, Justice Teehankee once again expressed his doubts on the validity of such an act. He categorically stated that “Such erosion by means of referendums of the whole structure and spirit of the Constitution for free contested elections and of the parliamentary system of government herein mandated should not receive the sanction of the Court.” Thus, Justice Teehankee showed his unwavering loyalty to rule of law and stood true to his oath of office to uphold the Constitution.

Justice Teehankee from his early years was a stout defender of human rights and many of his opinions, though originally dissents, became the majority rule. He had served as chairman of the Civil Liberties Union of the Philippines from 1950 to 1966, was the vice-chairman of the board of trustees of the Civil Liberties Union of the Philippines, Inc. and supreme commander of the Knights of Rizal. The United Nations Associations presented him with the Philippine Carlos P. Romulo Award, citing “his courageous and democratic adherence to the Rule of Law, espousal of democratic ideals and civil liberties, and respect for hunan rights, unmindful of the risks nd disadvantages attendant thereto during the regime of an authoritarian ruler; and his exemeplary government service characterized by unparallel competence and unquestioned integrity. The Concerned Women of the Philippines, in awarding Justice Teehankee with their Human Rights Award recognized “his relentless crusade against infringement of civil liberties by powerful forces, thus giving fuller meaning to constitutional guarantees on human freedom.”

Justice Teehankee consistently reminded all in his decisions that the Supreme Court stands as the guarantor of constitutional and human rights of all persons within its jurisdiction and must see to it that the rights are respected and enforced. Justice Teehankee’s values and ideals reached its culmination when he was sought to administer the oath of office of President Corazon C. Aquino at Club Filipino in San Juan at 10:00 a.m. at the height of the People Power Revolution, exactly two hours before President Marcos’s own presidential oath-taking at Malacanang before the serving Chief Justice at noon of February 25, 1986. During the Aquino Administration, Justice Teehankee would play a crucial role as adviser in the crafting of the 1987 Constitution and he was appointed chief justice of the Supreme Court of the Philippines.

After his mandatory requirement at the age of 70, chief Justice Teehankee was appointed Philippine ambassador and permanent representative to the United Nations in New York. On November 27, 1989, the Philippines lost one of its staunchest legal guardians when chief Justice Teehankee passed away in Manhattan, New York, from lung cuncer.

Chief Justice Teehankee was interred at the Libingan ng mga Bayani, a fitting resting place for a great man, who stood in the face of oppression, and in his gravestone is