[1][2] He was elected Member of Parliament for Mullingar in the Irish House of Commons in 1783, and went on to serve as Secretary of War in Dublin Castle administration.

[1] His efforts were greatly appreciated by King George III, who took the trouble to write to the Earl Marshall, "... so that his [Doyle's] zeal and exertions in our service may be known to posterity".

[6] Doyle started his military career in March 1771 when he purchased an ensigncy[7] and joined the 48th (Northamptonshire) Regiment of Foot.

[1] Doyle transferred to the 40th (2nd Somersetshire) Regiment of Foot on its being ordered overseas, where he served with distinction in the American War of Independence (1775–1783).

He was involved in the Battle of Long Island in August 1776, where he recovered the body of his commanding officer, Lieutenant-Colonel James Grant, under enemy fire.

[1] Raised in rank to brevet colonel, he led the unit under the Duke of York in the Flanders Campaign 1793–1795.

He served at the siege of Valenciennes 13 June-28 July 1793 and distinguished himself at Alost during Moira's retreat 1794 where he was wounded in a cavalry action, needing to return to Britain to recover.

[7]: 21  Brigadier General Doyle was then ordered to Gibraltar, however on his way to the port of embarkation was attacked by highwaymen and badly wounded twice.

[7]: 21–2 Confirmed in the rank of Brigadier General and appointed to command the 4th brigade, he served under Abercromby and Hutchinson in Egypt in 1801, and saw action at Manresa, Marabout, and Ramanieh 9 May.

[7]: 33 Doyle actively organised the defence in the Bailiwick of Guernsey, he oversaw the draining of land at Braye du Valle to connect the tidal north of the island to the main island, using the proceeds of the sale of the land to pay for the construction of military quality roads.

[5] In 1783 he was elected MP for Mullingar in the Irish House of Commons[1] Giving speeches to the Parliament of Ireland at Parliament House in favour of providing relief for starving unemployed Irish workers and their families, for which he was awarded the freedom of Dublin city, of improving the situation for disabled soldiers in Ireland, pleading the cause of foundlings and Catholic emancipation.

[10] George III wrote to the Earl Marshall, Charles Howard, 11th Duke of Norfolk: ... so that his (Doyle's) zeal and exertions in our service may be known to posterity.