After a failed attempt in 1945 he was first elected to parliament in 1950. After the election of the Diefenbaker government Hees was made Minister of Transport in 1957. In 1960 he moved to become Minister of Trade and Commerce. During this period Hees was regarded as the second most powerful man in the Tory party. However, in 1963 he had falling out with Diefenbaker and became embroiled in the Munsinger Affair and elected to sit out the 1963 election, which the Tories lost.
After considering a defection to the Liberals he returned to the legislature in 1965 as a Tory and remained in opposition for many years. When Brian Mulroney lead the party to a majority government in 1984 Hees was made Minister of Veterans Affairs. Hees retired from politics in 1988.