In April 1870, he left University to join the revolutionary movement of Timoteo Aparicio against the Colorado government of Lorenzo Batlle.

[citation needed] He wrote of the aim of the Revolution of Lanzas, in an article entitled "a tomb in the forest" published in the newspaper the Republic in 1872.

He signed the manifesto "Profession of a Rationalist Faith" in 1872, which asserted the immortality of the soul and the existence of the Supreme God in opposition to the Pope.

[citation needed] The three-month Revolutionary War was concluded in July 1872, and in Montevideo, Diaz began the militarization of the National Party.

[citation needed] He was made a senator by the National Party and took part in the second insurrection led by the nationalist Caudillo Aparicio Saravia, in 1897.