He succeeded to the title of his first cousin once removed, Thomas Fleming, 6th Baron Slane, in 1471.
He was one of the eleven Irish barons who came to Greenwich at Henry VII of England's summons in 1489; to their embarrassment, they were served at the table by the former pretender to Henry's Crown, Lambert Simnel, whose cause most of the Irish nobility including Lord Slane had supported.
The Irish nobility had been treated with similar mercy, and almost all of them received a royal pardon, but clearly, the King could not resist playing a joke on Simnel's former allies, who, he once remarked, would "Crown an ape" to gain more power.
Lord Slane married Elizabeth Welles, daughter of Sir William Welles (d. 1463), Lord Chancellor of Ireland,[1] and his wife Anne Barnewall; Elizabeth, who had previously been married to the second Baron Killeen, died in 1506.
Their children were: The Annals of Ulster state that James' death was due to the first recorded Irish outbreak of sweating sickness, Ireland having apparently escaped the first English epidemic of 1485.