He attended the University of Santo Tomas and completed a law degree at the Universidad Central de Madrid.

According to historian Ambeth Ocampo, De Leon, while in Spain, unsuccessfully sought courtships with Leonor Rivera and Leonor Valenzuela, who were then also two of the future Philippine national hero Jose Rizal's love interests, during which he confronted Rizal after finding out that the latter was engaged to both women at the same time.

[1][2] Upon his return to the Philippines, De Leon served as prosecutor (fiscal) of Barotac Viejo, Iloilo, and justice of the peace of his hometown of San Miguel.

[3] After the death of Senator Francisco Tongio Liongson in office, de Leon was elected in a special election on October 25, 1919, as his successor for the remainder of his term until 1922.

Their daughter Trinidad, was crowned as the Manila Carnival Queen in 1920[5] before marrying then-Capiz governor Manuel Roxas, and upon the latter's election as President of the Philippines, was first lady from 1946 to 1948.