Implementing his father's will, he gave his Irish title of Baron Hamilton of Strabane to his younger brother Claud.
His younger brothers inherited his father's Irish lands, while he received the Scottish ones, which he squandered away, being deep in debt in his later days.
On 10 April 1606 his father was created Earl of Abercorn and Lord Paisley, Hamilton, Mountcastell and Kilpatrick.
[9] On 8 May 1617, when he was only about 12 years old, he was created 1st Baron Hamilton of Strabane, in the peerage of Ireland, with remainder to the heirs male of the body of his father.
[2] The purpose of the creation was to give the Abercorns, who were Scottish earls but big landowners in Ireland, a seat in the Irish House of Lords.
Since his father had entailed his Irish lands on his younger brothers, he resigned the title of Baron Hamilton of Strabane on 11 November 1633.
He spent several years travelling the continent and visited Catholic countries, France and Italy, which encouraged him in his Catholicism.
James and Katherine had three sons, but the first two predeceased their father: Abercorn's problems with the Church of Scotland (the Kirk) began with the process engaged by the Paisley Presbytery against his mother and some of her servants.
The Bishop obtained a letter from the King, written by William Alexander, 1st Earl of Stirling that directed the church not to trouble her as long as she kept quiet.
[22] However, in April 1627 Abercorn returned from his travels on the continent and provoked the church by declaring himself openly a Catholic.
As the Duke had no sons, he was succeeded by his niece Anne Hamilton according to the succession rule of his title (see family tree).