During the Danish-Hanseatic War, together with his elder brothers Henry IV and Adolf VIII, he fought on the side of the Hanseatic League against Denmark.

In 1428, he took part as commander of the city fleet in the attack of Flensburg and the bombardment of Copenhagen by the Hanseatic League.

On 2 June 1432, Gerhard VII married Agnes, the daughter of Margrave Bernard I of Baden.

It was fairly clear that she must have been pregnant on the day of her wedding, giving rise to rumours that the children might not have been Gerhard's.

To stop these rumours, Gerhard VII declared in Schleswig Cathedral that he was the father, and that he'd secretly slept with his future wife before the wedding, and that she'd been a virgin then.