He possibly did his elementary studies in the city of Buenos Aires, and began his military career at the age of nineteen or twenty, serving in the Guardia del Juncal, a fortress built in the town of Cañuelas to prevent the advance of the Indians.

He lent his oath on February 12, 1780, before the dean councilor of the Cabildo de Buenos Aires Don Gregorio Ramos Mexía.

In 1780 the Consejo de guerra of Buenos Aires had appointed to Captain Casimiro Alegre, to lead one of the punitive expeditions against the "unfaithful Indians", who carried out a massacre against the inhabitants of the town of Luján in the night of August 27 of that same year.

In 1795 he was commissioned by the Viceroy, Pedro Melo de Portugal to make the appraisal of a land located in the current territory of Marcos Paz.

[11] His work as mayor of the brotherhood consisted mainly in the control of the rural areas of the Province of Buenos Aires, also exercising administrative and judicial tasks, and the persecution of the bandits.

[14] He served in the urban militias of the province of Buenos Aires for more than forty years, obtaining his retirement from the Argentine Army on September 17, 1817.

[24] In 1837 his son Saturnino Alegre Espinosa, sold a plot of 225 hectares to its neighbor Hannah Brocksopp, a female landowner of English origin.