Originally intended for the bar, Doyle soon transferred to the army and served in the American war where he became closely connected with Lord Rawdon (later Earl of Moira). On his return to Ireland he went on half-pay and was brought into the Irish parliament for Mullingar by the Earl of Granard, an opposition peer, who controlled four seats and whom government was naturally concerned to secure. Doyle for his part was anxious to return to active service and in 1788 the lord lieutenant pressed very strongly for military promotion for him in the hope, thereby, of winning over Granard. Although Pitt backed the application, the King would not concede it
Doyle was soon drawn back into politics by the appointment of Earl Fitzwilliam as viceroy of Ireland in January 1795. Among the victims of Fitzwilliam’s purge of government offices was Edward Cooke, military under-secretary, whom Doyle replaced. This administration was short-lived, and after Fitzwilliam had been supplanted by Camden in March, Cooke was soon restored to office, although Doyle may have already resigned on his own initiative when it became clear that the new administration intended to reverse Fitzwilliam’s pro-Catholic policy.
After the Union Doyle does not appear to have sought a seat in the Imperial Parliament. He became lieutenant-governor of Guernsey in 1803. Thence he confided to William Drummond his wish for a red ribband, 30 Oct. 1804, being confident that Pitt ‘will scorn to set off against my honest services any former political delinquency’.
At Westminster Doyle soon proved his ability in debate. In his conventional maiden speech, 22 Dec. 1806, he seconded the vote of thanks to the victors of Maida, but on 23 Jan. 1807 he obtained good-humoured attention for a speech on the army estimates delivered from the opposition bench. (He denied that he sat there as a spy, or because he was one of those Members who could not get ‘good places’ on the other side.) He gave credit to Windham’s military plans, to the disadvantage of Pitt’s, insisting on their professional superiority. But his best effort was to come: on 23 Feb. he warmed to the abolition of the slave trade. His early experience of slavery in South Carolina had made an indelible mark on him: ‘taught by that Power that pities me, I learned to pity them’. How much more excuse there was for a highwayman than for a slave dealer:
The robber may be compelled by hunger; besides, he risks his life in the attempt, and he has not the presumption to say, that he benefits those he robs; moreover, he does not ask compensation for giving up the trade.
He brushed aside the complacent reports of the average colonial governor on the humane treatment of slaves:
Everything he hears must be through an interested medium. On his visits he would see nothing but cheerfulness. Every face, whether white or black, would be dressed in holiday smiles—he would never hear the secrets of the prison house. Besides, the domestic slaves and the artisans, being under the immediate eye of the master, are free from the tyranny of the driver.
He paid tribute to the ministry for sponsoring abolition and to Wilberforce for his long campaign for it. On 12 Mar. 1807 he rose late, in an impatient House, to oppose Castlereagh’s amendment to the mutiny bill, intended to make a loophole in favour of prolonged service in the army by means of a recruitment oath. He voted for Brand’s motion following the dismissal of the ministry, 9 Apr. On 16 Apr. he hailed the capture of Montevideo, in which his own regiment had played a signal part.
Doyle’s parliamentary career ended with the dissolution of 1807. He remained lieutenant-governor of Guernsey (not governor, as he would have wished). It would appear, too, that he was disappointed of the Peninsular command awarded to Sir Arthur Wellesley. On 12 July 1811, in a memorial of his services intended for the Prince Regent, he mentioned seven wounds and nine expressions of gratitude from his commanders in 40 years’ military service in all climates. His only wish was for the order of the Bath.