Senator Sumulong was born on September 5, 1905 in Antipolo, Rizal to Don Juan Sumulong and Salome Sumulong.
He finished his elementary and high school education in public school in Antipolo, Rizal and in the City of Manila, except for two years of primary education which he spent in La Salle. He obtained his Associate of Arts degree in 1926 from the University of the Philippines and finished his law course at said State University in 1929, magna cum laude and topping the bar examinations. Several years thereafter, he obtained master of laws degree from Harvard Law School in the United States in 1932.
Senator Sumulong started his political career during his college days as a law student, when he was elected number one councilor in Antipolo, Rizal. He was elected congressman for the second district of Rizal in 1946 to 1949 and was elected Senator in 1949 and reelected in 1955 to 1961, 1961 to 1967, 1969 up to 1972. As a lawmaker, he was chairman of the Senate committee on Foreign Relations and headed the Buenavista-Tambobong scandal investigation committee. After that investigation, the Senate decided to create the Blue Ribbon committee for the purpose of exposing and thereby helping in eradicating graft and corruption in the government and became the first chairman of the said committee. Senator Sumulong was the chairman of the committee on the Executive of the 1986 Constitutional Commission.
Senator Sumulong also represented the Philippines in international conferences like Interparliamentary Union in 1951, Philippine Economic Mission in 1954 and the UN general Assembly in 1946, 1958, 1960, 1963 and 1965.
He was married to Estrella Rodriguez with whom he had six children.