Senator Pelaez was born in Medina, Misamis Oriental on November 30, 1915 to Gregorio Pelaez, Sr. and Felipa Neri.
He graduated valedictorian at Cagayan de Oro Elementary School and received highest honors at the Ateneo de Manila High school. He obtained an Associate of Arts degree in Cebu, UP Junior College and graduated Bachelor of Laws at the University of the Philippines in 1938 and topped the bar examinations.
Senator Pelaez worked as a Senate Clerk at the Journal Division from 1934 to 1935, Debate Reporter from 1935 to 1937, and court translator from 1937-1938. He was employed as assistant court reporter at the Court of Appeals from 1939 to 1940, then later Special Prosecutor from 1945 up to 1946. Senator Pelaez practiced law and at the same time professor of law at the University of Manila from 1946 up to 1963.
He was elected representative for Misamis Oriental for two terms from 1949 to 1953 and from 1965 up to 1969.He was elected Senator from 1953 to 1960. In 1961 up to 1965 he was elected Vice-President of the Philippines; then Secretary of Foreign Affairs from 1961 up to 1965, and from 1979 up to 1984 he was Assemblyman and Minister of State.
As a lawmaker he was chairman of various Senate committees and unanimously chosen “ Most Outstanding Senator “ by two organizations, the League of Women Voters of the Philippine and the Senate Press Club.
Aside from all the aforementioned positions, Senator Pelaez was Chairman and/or ranking member of Philippine delegations to various international conferences among which were: the UN 10th Commemorative Conference at San Francisco in 1955; the UN General Assembly meeting in 1957 and 1962; Interparliamentary Union Conference at London in 1957; in Peru and the Cameroons in 1972. He had been a member, consultant body of the Philippine Delegation to the SEATO in 1963 and panel/member at the RP-US Military Bases Negotiation in Washington, D.C. in 1975.
He married Edith Fabella with whom he has eight children.