His father, the late Senator Juan B. Alegre,[5] was at one time the biggest abaca planter and coconut plantation owner of the Philippines with his holdings extending from Sorsogon to the inland of Masbate, off the coast of southern Luzon and cattle ranches covering the island of Ticao, Masbate province.

Upon his father's death in 1931 Alegre was urged by Sergio Osmeña to campaign for the acceptance of the Hare-Hawes-Cutting Independence Act.

Alegre got himself introduced to politics in 1932 as a result of the organization of a youth party composed of men and women of liberal tendencies.

This became a nationwide political organization known as Young Philippines,[11] with his fellow Bicolano Wenceslao Vinzons[12] as president, and Alegre as vice-president.

The party's roster included Arturo Tolentino, Lorenzo Sumulong, Diosdado Macapagal, Domocao Alonto, Jose Laurel Jr., and many others who all became prominent figures in Philippine politics.