He graduated in 1904 from the Faculty of Medicine of the UBA University of Buenos Aires, that same year he presented a thesis about "The proof of the chloride".

[clarification needed] Back in Paraguay, he became director of the Hospital de Clínicas, and a substitute professor of Pediatrics.

[1] He assumed the first magistracy, in his character of Vice President,[2] after the death of Manuel Franco, a position that he held from June 6, 1919 until August 1920.

After World War II, the government of Montero was affected the economical crisis that had expanded through the entire region.

During his government some forts were founded in Chaco, the Caballero State was acquired, the municipal constitutional law was modified, the colony Nueva Colombia was founded, the project for postal charges to United States was approved, Paraguay was invited to participate in the International Rural Congress of Peoria (Illinois, USA).

In 1919 more than 100.000 pesos were used for building schools in the interior of the country, the agreement about the arbitrage with Uruguay and Eladio Velázquez was appointed member of the Supreme Court.

Also that year, the commercial agreement with Japan was signed, the law of trial and dismissal of magistrates; sanitary zones in Asunción, Villarica and Caacupé and was created the regulations for the Army.

Here is important to mention the hiring of the Brazilian Doctor Edgar Roquette Pinto and the retiring of Juan E. O'Leary in the Colegio Nacional and the Escuela Normal.