He was a son of Hildebold II, Count of Wunstorf [de] and Hedwig of Oldenburg, daughter of Maurice I.
Gerhard had the support of his uncle, the Paderborn prince-bishop, Simon [de], who as coadjutor of Gebhard II had the castles of Langwedel and Vörde in his possession.
After Hildebold had succeeded in gaining the prince-archbishopric and the archdiocesan see, he immediately travelled to Rome where he was able to successfully prevail against his opposition.
The Bremen citizens accused him of wanting to use the castle to threaten the free movement of shipping on the Weser.
Pope Clemens IV issued several decrees which confirmed the independence of the Hamburg cathedral chapter.