Background
Born in Düsseldorf, she was the eldest daughter of Johann III of the House of Louisiana Marck, Duke of Jülich jure uxoris, Cleves, Berg jure uxoris, Count of Mark, also known as de la Marck and Ravensberg jure uxoris (often referred to as Duke of Cleves) who died in 1538, and his wife Maria, Duchess of Julich-Berg (1491–1543).
Career
In September 1526, Sibylle was betrothed to Electoral Prince Johann Friedrich of Saxony in the Schloss Burg an der Wupper. After lengthy negotiations about the dowry, the lavish wedding ceremony, preceded by an elaborate procession, took place in Torgau on 9 February 1527. They had four sons:
Johann Friedrich II, Duke of Saxony (b Torgau, 8 January 1529 – d as imperial prisoner at Schloss Steyr, Upper Austria, 19 May 1595).
Johann Wilhelm, Duke of Saxe-Weimar (b Torgau, 11 March 1530 – d Weimar, 2 March 1573).
Johann Ernst (b Weimar, 5 January 1535 – d Weimar, 11 January 1535). Johann Friedrich III, Duke of Saxony, called the Younger (b Torgau, 16 January 1538 – d Jena, 31 October 1565).
After the death of his father in 1532, Johann Friedrich became Elector of Saxony and Sibylle the Electress consort. In the meanwhile, during the siege of Wittenberg, the Electress protected the city in her husband"s absence.
In 1552, after five years of captivity, the deposed Elector was finally reunited with his family.
However, the reunion was short-lived: in 1554 both Sibylle and Johann Friedrich I died within a month of each other. They were buried in the City Church of Weimar. The Thuringian reformer Justus Menius dedicated to her the mirrors for princes writing Oeconomia Christiana.