Complex sentence: St Leger was a Whig in politics, and this, backed by the support of influential friends and that of his brother Lord Doneraile was considered sufficient qualification for appointment to the Bench, and he became a Baron of the Court of Exchequer (Ireland).
Split into simpler sentences: St Leger was a Whig in politics, and this, backed by the support of influential friends and that of his brother Lord Doneraile was considered sufficient qualification for appointment to the Bench. He became a Baron of the Court of Exchequer (Ireland).