Mariano Hugo, Prince of Windisch-Graetz (German: Mariano Hugo, Fürst zu Windisch-Graetz, Italian: Mariano Ugo, Principe di Windisch-Graetz; born 27 July 1955) is the current head of the Austrian, or Italian, House of Windisch-Graetz. A former ambassador of the Sovereign Military Order of Malta (SMOM) to the Republic of Slovakia, he is currently ambassador of the SMOM to Slovenia.
Windisch-Graetz was born in Trieste as the elder son of Maximilian Antonius, Prince zu Windisch-Graetz and Maria Luisa (Marlise) Serra di Gerace. His mother was the legitimatised daughter of Gian Battista Serra, 12th Principe di Gerace by Donna Maria Grazia Carafa d'Andria.
Windisch-Graetz was educated firstly in Rome at the school of the De La Salle Brothers and then in England at the University College of Buckingham, from which he graduated in 1975 with a degree in economics and political science.
When his father died in 1976, Windisch-Graetz succeeded as head of a cadet branch of the House of Windisch-Graetz, a mediatised house whose members historically bear the style of Serene Highness.