De Leon produced a number of anti-American propaganda films during World War II, in collaboration with the occupying Japanese forces and Japanese director Yutaka Abe, who personally chose De Leon for the projects.

De Leon was arrested and charged with treason after the Japanese were defeated, and was almost executed by the Filipino government.

[5] All of the films for which he won Best Director also won Best Picture at the FAMAS, namely Sawa sa Lumang Simboryo (1952), Hanggang sa Dulo ng Daigdig (1958), Huwag Mo Akong Limutin (1960), Noli Me Tangere (1961, adapted from the novel of the same title), El Filibusterismo (1962), Daigdig ng Mga Api (1965), and Lilet (1971).

Vallejo was a pre-war era actress who played a starring role in his directorial debut movie Bahay-Kubo (1939).

Together they have 2 children, Liberty Ilagan (July 6, 1943–2020)[7] and Maria Fe "Baby" (born 1949), the widow of actor Ronaldo Valdez.