Machado de Assis is linked to Romanticism in the first part of his career and to Realism in the second, and criticism usually marks the turn with The Posthumous Memoirs of Brás Cubas, published in book form in 1881.
In the first phase are the novels Resurrection (1872), The Hand and the Glove (1874), Helena (1876), and Iaiá Garcia (1878), of more conventional plot and with romantic traits, along with his first books of poetry and stories. In the second phase come The Posthumous Memoirs of Brás Cubas, Quincas Borba, Dom Casmurro, Esau and Jacob, and Counselor Ayres' Memorial, in which irony and criticism of society move to the center. The first three of this list form what is called the Realist Trilogy.
The biography published by the Brazilian Academy of Letters itself notes that the masterpieces of this phase escape any literary school label, and Wikipedia speaks of a heterodox realism. In other words, the label Realism indicates the period, not a mold that Machado followed to the letter. In poetry he also passed through Indianism, in Americanas, and through Parnassianism, in Ocidentais.
On Clavis: The Posthumous Memoirs of Brás Cubas, Quincas Borba.