As one of the "lords ordainers" he was a recognized leader of the opposition to Edward II.
The leader of the Opposition from the first denounced the diplomatic steps taken by Lord Milner and Mr Chamberlain, and objected to all armed intervention or even preparation for hostilities.
He was an ardent leader of the opposition to the Stamp Act, advocating even then a separation of the colonies from the mother country; and in the Continental Congress of 1774 he discussed the situation on the basis of inalienable rights and liberties, and urged an immediate attack on General Thomas Gage, that he might be defeated before receiving reinforcements.
After the death of George Ponsonby in 1817 Tierney became the recognized leader of the opposition in the House of Commons.
In his place Cecil Rhodes, then leader of the Opposition in the Cape parliament, was sent to Bechuanaland.