To placate him, Charles VI, Holy Roman Emperor (Maria Clementina's own maternal first cousin) had her arrested while on her way to Italy to marry James Francis Edward.

She was confined in Innsbruck Castle but eventually the guards were deceived and, with the help of Charles Wogan, Maria Clementina escaped to Bologna, where, for safety from further intrusions, she was married by proxy to James, who was in Spain at that time.

Maria Clementina and Prince James were formally married on 3 September 1719 in the chapel of the episcopal palace of Montefiascone, Italy, in the Cathedral of Santa Margherita.

[4] Following their marriage, James and Maria Clementina were invited to reside in Rome at the special request of Pope Clement XI, who acknowledged them as the king and queen of England, Scotland and Ireland.

The Pope provided them with a papal guard of troops and gave them the Palazzo Muti in the Piazza dei Santi Apostoli in Rome to live in, as well as a country villa at Albano.

Popes Clement XI and Innocent XIII considered James and Maria Clementina, both Catholics, the rightful king and queen of England, Scotland and Ireland.

[5] She was prone to depression, spending much of her time praying and submitting to religious fasting and other Catholic ascetic rituals, which is thought to have played a role in the fact that she never conceived again.

Pope Benedict XIV commissioned architect Filippo Barigioni to design a monument for her memory, Pietro Bracci sculpted a statue for it, and it was erected 1742 in the Basilica.