The granddaughter of John III Sobieski, she was one of Europe's wealthiest heiresses. Princess Maria Klementyna was betrothed to Prince James Stuart. King George I of England was opposed to the marriage because he feared that there would be an heir and, in order to placate him, the Austrian Emperor, Charles VI arrested Princess Maria Klementyna while on her way to Italy to marry James Stuart. She was confined in Innsbruck Castle but eventually the guards were deceived and Maria Klementyna escaped to Bologna, Italy, where, just to be safe from further intrusions, she was married by proxy to James who was in Spain at that time. Maria Klementyna's father, Prince James Louis Sobieski, approved her escape declaring that, as she became engaged to Prince James she ought to "follow his fortune and his cause".
Maria Klementyna and James Stuart were formally married on September 3, 1719 at Montefiascone, Italy in the Cathedral of Santa Margherita. Following their marriage, James and Maria Klementyna were invited to reside in Rome at the special request of Pope Clement XI, who acknowledged them as the (Catholic) King and Queen of Britain. The Pope provided them with a papal guard of troops, gave them the Palazzo Muti in the Piazza dei Santi Apostoli in Rome to live in, plus a country villa at Albano. The Catholic Church also provided them with an annual allowance of 12,000 crowns out of the papal treasury.
Princess Maria Klementyna and James Stuart had two sons:
Maria Klementyna died at the early age of 32 on January 18, 1735. She was interred with full royal honors in St. Peter's Basilica in the Vatican. Pope Benedict XIV commissioned Pietro Bracchi (1700-1773) to sculpt a monument to her memory to be erected in the Basilica.