Stevens was first elected to the House of Commons in the 1911 general election as a Conservative and served in the short lived Cabinets of Prime Minister Arthur Meighen in 1921 as Minister of Trade and Commerce and in 1926 as Minister of Customs and Excise.

He was an opponent of Asian immigration saying, in 1914, "We cannot hope to preserve the national type if we allow Asiatics to enter Canada in any numbers."

When R.B. Bennett took the Tories to victory in the 1930 general election he made Stevens his Minister of Trade and Commerce. In 1934 Stevens was chairman of a royal commission on price spreads in which he exposed abuses by big business, attacked corporate interests and called for radical reform. He then resigned from Cabinet when his recommendations were ignored and formed the Reconstruction Party of Canada to run in the 1935 Canadian election but was the only candidate to win a seat. He subsequently crossed the floor to rejoin the Conservative Party in 1938 and ran as a candidate in the 1940 Conservative leadership convention but was eliminated on the first ballot, losing to Arthur Meighen.

Stevens did not enter the 1945 general election, but ran again in Vancouver Centre in 1949 and again in 1953, losing both times.