Judith was born 19 May 1100, the eldest daughter of Henry IX, Duke of Bavaria and Wulfhilde of Saxony, daughter of Magnus, Duke of Saxony and Sophia of Hungary, and thereby a member of the powerful German House of Welf.

The Historia Welforum names in order Iuditham, Mahtildem, Sophium and Wulfildem as the four daughters of Henricus dux ex Wulfilde.

She had, in addition to her seven legitimate siblings, one half-brother, Adalbert, born of her father's relationship with an unnamed mistress.

The Historia Welforum specified that Judith married Friderico Suevorum duci, but did not mention the date.

The defection of Judith's father created an enmity between the Welfs and the Swabians that would have far-reaching consequences in Germany which would last throughout the 12th century.