 Irigoyen returned to public life in 1870 as a provincial legislator, and in 1875, was appointed Minister of Foreign Affairs by President Nicolás Avellaneda.He negotiated boundary treaties with Brazil and Paraguay in the wake of the Paraguayan War against the latter nation, and was named Internal Affairs Minister in 1879, during which tenure he drafted the 1880 federalization of Buenos Aires.He was returned to the Foreign Minister's post by Avellaneda's successor, President Julio Roca, and secured the boundary treaty of 1881 between Chile and Argentina.