He is best known for his 1906 socialist novel, Banaag at Sikat and for his contributions to the development of Filipino grammar and Tagalog orthography.

[2] His father was imprisoned during Philippine Revolution because Spanish authorities found copies of José Rizal's Noli Me Tangere and Ang Kalayaan in his possession.

Dominador Goméz was charged and sentenced by the Supreme Court of sedition and illegal association against the government in 1903, Goméz's labor group Union Obrera Democratica Filipina (Philippine Democratic Labor Union) was absorbed by Santos.

In 1903, Santos started publishing fragments of his first novel, Banaag at Sikat (From Early Dawn to Full Light) on his weekly labor magazine Muling Pagsilang (The Rebirth) and was completed in 1906.

Consequently, he was appointed to the 5th Philippine Legislature as senator from the twelfth senatorial district representing provinces having a majority of non-Christian population.

In 1940, Santos published the first grammar book of the "national language", Balarila ng Wikang Pambansa (Grammar of the National Language) which was commissioned by the Surian ng Wikang Pambansa (SWF).

He was also appointed to assist in the translation of inaugural addresses of presidents Jose P. Laurel and Manuel A. Roxas.