From his mother he inherited the Lordships Hondschoote, Houtkerque, Lokeren, Veurne and Sint-Winoksbergen.
Philip the Good besieged the English-held city and as Admiral of Flanders, it was John's task to block the harbor of Calais.
He sank 5 to 6 ships laden with stone in the harbor entrance, but the people of Calais were able to approach these wrecks during low tide and dismantled them.
After the siege, Humphrey, Duke of Gloucester led an expeditionary army into Flanders and English pirates plundered the Flemish coast.
Unable to stop these English raids, John of Horne was held accountable by the Flemish people and he was lynched in the dunes near Ostend.