Archduke Sigismund Franz was the last male Habsburg of the collateral Tyrolean branch of the dynasty.
As the younger son of Archduke Leopold V and Claudia de Medici he was at first intended for a career in the Church. At the age of sixteen he became bishop of Augsburg, in 1653 bishop of Gurk and in 1665 bishop of Trent. He was thus well endowed with rich ecclesiastical livings. Like his father, who also started out as a prince of the Church before becoming ruler of Tyrol, Sigismund Franz never received holy orders.
After the early death of his elder brother Ferdinand Karl (1662) he succeeded him as sovereign ruler of Tyrol. His reign began cautiously, with the aim of rehabilitating the finances of the land which were in dire straits after his brother’s inglorious rule.
In order to be able to continue the collateral Tyrolean line of the dynasty he resigned from all his ecclesiastical offices, returning to the secular state, and began the search for a suitable wife.
His choice settled on Hedwig Auguste von Sulzbach (1650–1681), a German noblewoman. However, before the marriage could be consummated Sigismund Franz died suddenly at the age of only thirty-five. With his death in 1655 Tyrol and the Austrian Forelands passed to Emperor Leopold I and were again united with the other Austrian patrimonial dominions.