José Maria de Eça de Queirós or Queiroz ((November 25, 1845 - August 16, 1900) is widely considered to be the greatest Portuguese writer in the realist style, and one of the greatest figures of European 19th century fiction (admittedly not its finest period, IMHO). Zola considered him to be far greater than Flaubert. Others rank him with Dickens, Balzac and Tolstoy. Eça never officially rejected Catholicism, but was very critical of the Catholic Church of his time, as is evident in his novels. This may sound rather timid sitting here in the early 21st century, but given the power of the church in the 19th century it represents remarkable courage.
He used the old-fashioned spelling "Eça de Queiroz" and this is the form that appears on many editions of his works; the modern standard Portuguese spelling is "Eça de Queirós". That would be a helpful clue for you to find his works, but you don't have to, we did.