He was born in Lichtenstein, then part of the Kingdom of Württemberg, at his family's Lichtenstein Castle, being the second son of Duke Wilhelm of Urach and his first wife Duchess Amalie in Bavaria.

After the war Karl Gero von Urach studied architecture, and later worked as an architect in Munich.

In 1928, on his father's death, Karl Gero became the third Duke (Herzog) of Urach, as his elder brother Wilhelm had resolved to marry morganatically (he was a director at Mercedes-Benz for most of his life, and had two daughters).

Until 1945 he was based at the local army headquarters at Tübingen and Ulm.

On 20 June 1940 Karl Gero von Urach married Countess Gabriele of Waldburg zu Zeil und Trauchburg (1910–2005).