Sir John was second son of William Stanley of Storeton, Master Forester of Wirral - he was a soldier with an exceptional military record and confident of Richard II who had appointed him deputy to Robert de Vere Lord Lieutenant of Ireland. He married Isabel of Lathom, in 1385, when he was 40 and, due to unexpected deaths of various closer heirs, received from her large estates in southwest Lancashire and Cheshire.
The Stanleys were adroit at joining the winning side and thus in 1399 he had joined Henry of Lancaster against Richard and, after Henry was crowned King, received several more estates in Cheshire.
In 1405 he was granted the Lordship of Man in return for his help in suppressing the rebellion in Wales led by the Percies. Legally this was not yet Henry's to give as the current Lord, Henry de Percy, had not yet been attainted - he actually had avoided being at Shrewsbury due to illness and managed to apologise his way out, saving his head but still losing the Island!. This legal error was to cause much trouble during the disputed inheritance of 1594 and the Island was re-assigned to the Stanleys in 1610.
Initially the grant of the Lordship was for his lifetime only, but in 1406 on payment of 1,300 marks (1 mark = 13s 4d - or for those younger than 40 £0.67) Henry granted it for posterity throwing in the captaincy of Castle Rushen, patronage of the bishropric of Sodor and Man as well as the various royalties etc. then worth some £400 per year for good measure!
In 1408 he was sent, as Lord Lieutanant, back to Ireland where he died in 1414. His body was returned to Lathom and buried in Burscough Priory near Ormskirk.