When General Justo José de Urquiza declared against the dictator Rosas in 1851, demanding implementation of a national constitution, Benavídez at first gave his support to Rosas and was designated military commander of the west. After the Battle of Caseros (3 February 1852), Benavídez adhered to Urquiza's cause and concurred with the San Nicolás Agreement on 31 May 1852.