He was a younger son of Count Rudolf II and Ita, a daughter of Duke Conrad I of Swabia of the Conradine dynasty.

[1] In the 1020s, Welf feuded with the Augsburg and Freising bishops.

[3] Welf opposed the election of the Salian count Conrad II as King of the Romans in 1024 because it did not suit his interests, but he had to eventually relent.

[4] The next year he joined a rebellion launched by the Babenberg duke Ernest II of Swabia, but finally submitted in 1027.

[7] Welf II was married to Imiza, daughter of Count Frederick of Luxembourg.