After the fall of the Austro-Hungarian Empire following the defeat of the Central Powers during the automn of 1918, Count Manfred resigned from all his official offices and spend his remaining years between his estates in Austria and his family's Czech estates (Teplice).
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In 1884, he married in Vienna Gräfin (countess) Franziska Pejácsevich von Veröcze, heiress of one of the most powerful family of the Croatian descending from the princes Esterházy von Galántha.
He was the eldest son of Count Christian Christoph Clam-Gallas (1771–1838), patron of Beethoven, and Countess Josephine Clary-Aldringen (1777–1828).
His great possessions descended to his sister, and thence to the family of Clary and Aldringen.