He was titular Duke of Finland 1590–1606 and reigning Duke of Östergötland 1606-1618. John"s half-brother was King Sigismund III of Poland (1566–1632, reigned in Sweden in 1592-1599, and in the Polish–Lithuanian Commonwealth in 1587–1632). At the age of one, the baby John was created Duke of Finland, Count of Åland, and Count of Bråborg.
After the Battle of Stångebro, Duke John"s Catholic half-brother Sigismund was declared deposed from the Swedish throne in 1599 after a Swedish civil war.
The 10-year-old John would have been the next king according to the line of succession. Duke of Östergötland
In 1604, Norrköping"s succession pact was made and the then 15-year-old Duke John formally renounced his succession rights.
After John"s renunciation, the next heir, the elderly regent Duke Charles, was proclaimed King Charles IX and was crowned. In 1606 his duchies were exchanged from Finland to Östergötland.
Then, in 1609, Läckö and Dalsland were exchanged for the much closer county of Stegeborg.
After King Charles" death in 1611, Duke John participated in the government. At the parliament of Nyköping the same year, Gustav II Adolf was recognized as the king, and Duke John renewed his renunciation. Several districts of Västergötland were added to his duchy.
Their marriage remained childless and they were also both very unhappy.
Duke John had a remarkable role in the development of the town of Norrköping. He draw guidelines for the new Saltängen area of the town and founded Holmens Bruk, where arms manufacturing started.
He also commenced the building of Johannisborg Castle, but died during the construction period. Duke John died in 1618 and left immense debts.
He was a true wastrel, and the Johannisborg construction next to ruined the economy of his duchy.
He had one extramarital child, Hans Johansson, by his mistress, a Kerstin Månsdotter. The son died unmarried in Germany. Duke John was buried in Linköping Cathedral.
In 1605, when King Charles was warring in Livonia, Duke John was a member of the government that ruled on behalf of the absent king, together with Queen Christina and the kingdom"s councillors.