Latouche succeeded to his father’s partnership in the family bank and to substantial estates in county Kildare. He sat in the Irish parliament for the family borough of Harristown and opposed the Union. Having lost his seat by disfranchisement, he succeeded his father in the representation of the county in 1802, with the good wishes of government who desired to conciliate his family, but also of the Duke of Leinster who was in opposition. On 4 Mar. 1803 he voted against government on the Prince of Wales’s finances and the viceroy soon afterwards reported that he and his brother John (known as Count and Discount) were among the Irish Members enticed by the Prince by means of ‘the dinners at Carlton House’: he repeated this view, 29 Feb. 1804:
The latter are both, as it appears to me great coxcombs, captivated last year by the Prince of Wales’s dinners, and not to be counted upon as friends of government ... The two ... go over tonight, undetermined as I hear, what part they shall take, but probably determined to vote as they did last year.
The Prince expected this too, and on 7 Mar. Latouche was in the minority on Wrottesley’s motion censuring the Irish government, and on 15 Mar. joined opposition in favour of Pitt’s naval motion.
Latouche supported the Grenville administration, though Fox had to make a personal appeal for his attendance in May 1806 after the viceroy had failed to budge him. It was feared that he was motivated in this by ‘coldness or disgust’ at government’s failure to find a place for his brother-in-law at the revenue board.