By 1194 he had become Constable of Jerusalem; the fact that he was the half-brother of Isabella, Queen of Jerusalem gave him considerable influence. He served as regent from 1205 to 1210 for Maria of Montferrat, Isabella's daughter. He was also a noted jurist.
John was married twice. His first wife was Helen of Nephin, by whom he had one son, Balian, Lord of Beirut (d. 1247). In 1207 he married Melisande, Lady of Arsur. They had at least one son, John of Arsur (c.1211-1258).
John of Ibelin (1215-1266), count of Jaffa and Ascalon and a noted jurist, was the nephew of the first John of Ibelin. He was the son of John's brother Philip of Ibelin, Bailli of Cyprus, and Alice of Montbéliard.
This John of Ibelin was a contributor to the Assizes of Jerusalem, the code of laws enacted for the government of the Kingdom of Jerusalem. His contribution was the Livre des Assises de la Cour des Barons.