In November 1414, he was elected Knight of the Shire and a Justice of Chester. He served in the French Wars, being part of a considerable contingent from Lancashire which accompanied Henry V in the campaign which ended at Agincourt in 1415.

His father, the first ruler of the Stanley line, never visited the Isle of Man. Sir John, however, took a keen interest in his kingdom, visiting it on several occasions, with beneficial results for the island. He began the first systematic record of the history of Man, and he introduced written laws for the first time, drawing up a sort of Magna Carta defining the rights and duties of King, Church and People. Sir John also substituted trial by jury for trial by combat.

In 1428, Sir John was made Constable of Caernarvon Castle and Sheriff of Aglesey in 1439, when he secured peace in Wales and loyalty to the English King.

• Married: 1404

1. Thomas Stanley b: 1405