The nephew of Mosé Bianchi, Mariani was also born in Monza and studied in Milan. He visited Egypt in 1881-2, but his early successes were achieved with subjects drawn from the Lombard landscape, particularly sporting scenes around Zelada. In the 1880’s he won medals at the Paris Salon and in Munich.
From the 1890s onwards he travelled frequently to Bordighera where he painted a series of atmospheric marine views. At the same time he became fascinated by the fashionable life of Monte Carlo, and for the rest of his career was a frequent visitor, depicting elegant women promenading or at the gambling tables.