Sixtus' father had been deposed from the Duchy of Parma during the wars of Italian unification, but having inherited the large fortune of his childless uncle, Henri, Count of Chambord, Duke Robert was very wealthy.

Prince Sixtus was educated at Stella Matutina, a Catholic boarding school for boys run by Jesuits in Feldkirch, near the Swiss border.

On the death of his father in 1907, the largest part of the family's fortune was inherited by Elias, Duke of Parma, the only healthy son among Sixtus' half-siblings.

Charles agreed, in principle, to the first three points and wrote a letter dated 24 March 1917, to Sixtus giving "the secret and unofficial message that I will use all means and all my personal influence" to the French President.

When news of the overture leaked in April 1918, Sixtus's brother-in-law, Charles I of Austria, denied involvement until French Prime Minister Georges Clemenceau published letters signed by him.

The marriage lacked the authorization of Sixtus's elder half-brother, Elias, Duke of Parma, and was considered non-dynastic until 1959, at which time Elias's son, Robert Hugo, Duke of Parma, inheriting his father's position as head of the family, recognized the marriages of his uncles Sixtus and Xavier.

Together, they had one daughter: Princess Isabella (1922–2015) who married a distant cousin Count Roger de la Rochefoucauld on 23 June 1943.

As Sixtus's half-brother, Elias, had served in the Austrian army, the French government expropriated Chambord castle, owned by the Bourbons of Parma.

[1] In the following years he made several exploratory expeditions to Africa, wrote a number of books (including a biography of his great-great grandmother Maria Luisa of Spain, Duchess of Lucca) and treatises.