From 1292, there was an inheritance dispute in the House of Hesse, between Henry's sons from his two marriages, as his second wife demanded a share for her own children.

His half-brother Otto I received the Land of the Lahn, the later Upper Hesse, with the capital Marburg.

In 1309, John conquered the city and forced Duke Albert II of Brunswick-Göttingen to accept his repayment.

Emperor Henry VII appointed him protector of the free imperial cities of Mühlhausen, Nordhausen and Goslar.

In 1306, John married Adelaide of Brunswick-Lüneburg, the daughter of Duke Albert II of Brunswick-Göttingen.