John Irwin was page of honour to Lionel, 1st Duke of Dorset, lord lieutenant of Ireland 1730-7; and thus began a connexion with the Sackville family which lasted throughout his life. He was returned to Parliament on the Sackville interest at East Grinstead; and became the closest friend of Lord George Sackville, whose political line he followed implicitly, voting with Opposition till 1774 and afterwards with Government. Only one speech by him (on a trivial matter) is recorded.
Burke called him ‘a good humoured, well behaving man’;
He saw service on the coast of France in 1758, and later with Prince Ferdinand in Germany. His regiment was disbanded in 1762, and for three years he was without military employment. On 19 June 1765 Thomas Whately wrote to Grenville:
General Irwin has been offered to go to Gibraltar: he is much mortified at this turn ... as it is a situation very different from that he hoped for, and he fears may be given him instead of a regiment. It has, however, been put to him in such a way that he finds he must accept it.
He was promoted to a regiment on his return in November 1767, and at the general election of 1768 unsuccessfully contested Kinross. In 1775, probably through the influence of Lord George Germain (as Sackville had become), he was given the command in Ireland. When affairs became difficult in that country, North wrote to the King, 27 June 1779:
Lord North thinks himself obliged to repeat to his Majesty that he finds in every quarter that Sir John Irwin, though well esteemed as a gentleman, is in no great estimation as a general, and the world is very uneasy about his having the command in Ireland in such a perilous moment as the present.
To remove him, thought the King, ‘would be disgracing an amiable man’; but ‘if the advice had been to send a good general below him to his assistance that might have deserved attention. Irwin is practicable and would hear advice.’
‘No income, however large’, wrote Wraxall,
