Mariano Hugo, H.S.H. Prince of Windisch-Graetz, Bailiff Grand Cross of Honour and Devotion in Obedience, Grand Cross of the Order “pro Merito Melitensi” of the Sovereign Military Order of Malta, was born on July 27, 1955, in Trieste. He is the son of H.S.H. Maximilian Antonius, Prince of Windisch-Graetz, Bailiff Grand Cross of Honour and Devotion, and H.S.H. Princess Maria Luisa “Marilise” Serra di Gerace – Carafa d’Andria, Dame of Grand Cross of Honour and Devotion.

He was educated in Rome at the school of the De La Salle Brothers. In 1975 he graduated from University College of Buckingham with a degree in Philosophy, Economics and Political Science.

In 1976, at the age of 21, he became the head of the Windisch-Graetz family.

In 1984, His Holiness Pope John Paul II appointed him Gentleman of His Holiness, one of the highest civilian ranks in the Roman Catholic Church. Prince Mariano Hugo is a Knight of Honour and Devotion in Obedience of the Sovereign Military Order of Malta, a Grand Officer pro Merito Melitensi, a Knight Grand Officer of the Order of the Holy Sepulchre, a Knight of Justice of the Sacred Military Constantinian Order of Saint George, a Knight of the Collar of the Supreme Order of the Most Holy Annunciation, and a Knight Grand Cross of the Order of Saints Maurice and Lazarus.

On February 11, 1990, in Salzburg, Austria, he married H.I.R.H. Archduchess Sophie of Austria, daughter of Archduke Ferdinand and Archduchess Helen (born Countess of Toerring-Jettenbach).

In 1997, Prince Mariano Hugo founded the Windisch-Graetz Foundation, which focuses on humanitarian aid for the poor, the sick, and the Catholic Church. The foundation has notably funded life-saving initiatives, including aiding children injured by landmines during the wars in Serbia and Kosovo.

On November 30, 2000, H.I.R.H. Archduke Otto of Austria bestowed upon him the Knight of the Golden Fleece.

In 2003, Windisch-Graetz was appointed Ambassador of the Sovereign Order of Malta to the Republic of Slovakia; in 2009, he was appointed Ambassador of the Sovereign Order of Malta to the Republic of Slovenia.