First elected as a Conservative MP from New Brunswick in the 1921 general election, Hanson served continuously in the Canadian House of Commons until his defeat in 1935. He had been appointed to the Cabinet of R. B. Bennett in 1934 as Minister of Trade and Commerce.
In 1940 he returned to Parliament despite the poor showing of the Conservatives in that election and the personal defeat of Robert Manion who resigned two months after the election. The Conservative caucus chose Hanson as interim leader and he served as Conserative party leader until Arthur Meighen was elected the new party leader in November 1941. As Meighen did not have a seat in the House (and then failed to win a seat through a by-election), Hanson continued as Leader of the Opposition until 1943.