Mary was born in Vianden in February 1491[1][2][3] as the second daughter and sixth and youngest child of Count John V of Nassau-Siegen and his wife Landgravine Elisabeth of Hesse-Marburg.

[4][5] Her family spent most of the time there from 1489 onwards, because to get to know these new areas and to include them in his administration, Mary's father had to stay there for longer periods.

It was a double wedding, on the same day Mary's elder sister Elisabeth married to Count John III of Wied [de].

[8] Mary's husband was the son of Count John IV of Holstein-Schauenburg-Pinneberg and his wife Lady Cordula of Gemen.

[1][2][note 3] She had nine children including Adolf III of Schauenburg, Archbishop of Cologne from 1547 to 1556, Anton of Schauenburg, Elector and Archbishop of Cologne from 1556 to 1558 and Otto IV of Schaumburg (1517-1576), co-ruler from 1531 to 1560, ruling Count of Holstein-Schauenburg from 1560.