In 1780, he entered the Irish House of Commons as the member for Trim until the following year when, at his father's death, he became 2nd Earl of Mornington, taking his seat in the Irish House of Lords. He was elected Grand Master of the Grand Lodge of Ireland in 1782, a post he held for the following year. Due to the extravagance of his father and grandfather, he found himself so indebted that he was ultimately forced to sell all the Irish estates. However, in 1781, he was appointed to the coveted position of Custos Rotulorum of Meath.