He represented Stanstead in the Canadian House of Commons from 1930 to 1935 and from 1945 to 1949 as a Conservative and then as a Progressive Conservative member. He sat for the Victoria division in the Senate of Canada from 1955 to 1956. He was Batonnier of the Bar Association of Montreal and also President of the Canadian Bar Association, from 1947 to 1948.
He was also president of the Stanstead County Historical Society and a lieutenant in the militia.
In 1948, while serving as the President of the Canadian Bar Association and Member of Parliament for Stanstead, Hackett spoke in the House of Commons against a proposal that the position of chief commissioner of the Board of Transport Commissioners be designated as open only to a judge of the Exchequer Court of Canada. Hackett was concerned that the proposal would blur the lines between the quasi-political and policy role of the Board, compared to the traditional neutrality of judges, and could undermine popular respect for the judiciary as neutral arbiters.
Hackett died in office at the age of 72.
Conservative Party of Canada, Progressive Conservative Party of Canada.
Hackett served as a member of the board of governors for McGill University.