Rodó spent most of his life in Montevideo, devoting himself to writing, voracious reading, teaching, and political activity. In 1895 he helped found the Revista nacional de literatura y ciencias sociales (“National Review of Literature and Social Sciences”), and from 1898 he was professor of literature at the national university (University of the Republic) in Montevideo. He also served as director of the National Library of Uruguay. Twice, in 1902 and 1908, he was a member of the Chamber of Deputies.

In the essay generally considered to be his masterpiece, Ariel (1900), Rodó set forth his moral credo. Concerned with patterns of human life and with both personal and political conduct, Rodó maintained that individual self-scrutiny is the basis for enlightened action for the good of all. Próspero, the venerable teacher in Ariel, cautions his young listeners not to be impressed by material triumph but to use their own spiritual, moral, and intellectual resources to strive for a well-rounded life. Warning against what he saw as North American materialism, Rodó called for idealism from young Spanish Americans to bring forth the best features of democracy. This essay, which brought Rodó international recognition and is today considered one of the most influential works of philosophy written in Spanish America, has been called by one critic “the ethical gospel of the Spanish-speaking new world.”

Rodó's other writings include Motivos de Proteo (1908; The Motives of Proteus) and El mirador de Próspero (1913; “The Gallery of Próspero”), a series of essays on some of the outstanding figures of Spanish America. In 1916 Rodó left Montevideo to travel in Europe, where he died.