The Philippine constitutional plebiscite of 1973 ratified the 1973 Constitution of the Philippines.
In 1970, delegates were elected to a constitutional convention which began to meet in 1971. In September 1972, President Ferdinand Marcos declared martial law and arrested 11 members of the convention. The convention then re-convenened wrote a constitution in line with what dictator President Ferdinand Marcos wanted.
Marcos issued Presidential Decree No. 86 calling for the cancellation of the plebiscite and instituted barangays' citizens' assemblies to ratify the new constitution by a referendum from 10–15 January 1973.
On 17 January 1973, Marcos issued Proclamation No. 1102 certifying and proclaiming that the 1973 Constitution had been ratified by the Filipino people and thereby was in effect.
These results were challenged by the Ratification Cases heard by the Philippine Supreme Court in 1973. The court upheld the results and the ratification of the 1973 Constitution.
For this plebiscite to changes to voting requirements were implemented. The voting age was reduced from 18 to 15 years old and those who were illiterate were allowed to vote.