A member of the House of Wittelsbach, Alexander Sigismund von der Pfalz-Neuburg was born in Neuburg an der Donau on April 16, 1663, the fifth son of Philip William, Elector Palatine and his wife Landgravine Elisabeth Amalie of Hesse-Darmstadt.
At the time Alexander Sigismund was born, his father was Herzog of Palatinate-Neuburg. His father became Elector Palatine in 1685) He was destined for the clergy from a young age, and was sent to study with the Jesuits in Neuburg an der Donau and Düsseldorf. He was appointed coadjutor bishop of Augsburg on February 10, 1681.
He suffered a serious riding accident in 1688.
He was ordained as a priest on July 26, 1689. Johann Christoph von Freyberg-Allmendingen died on April 1, 1690 and Alexander Sigismund succeeded him as Prince-Bishop of Augsburg, with Pope Alexander VIII confirming his appointment on May 31, 1690.
He was consecrated as a bishop by Marquard Rudolf von Rodt, Bishop of Constance, on June 18, 1690. In 1714, Alexander Sigismund suffered a bout of mental illness, and the cathedral chapter of Augsburg Cathedral selected Johann Franz Schenk von Stauffenberg, Bishop of Constance, to be coadjutor bishop on June 11, 1714.
Alexander Sigismund finally recovered enough to resume his duties as Prince-Bishop in 1718.
He died in Augsburg on January 24, 1737.
