Doi began his political career at the 1950 Hawaii State Constitutional Convention that drafted the first state laws for Hawaii that went into effect in 1959. During that Convention, Doi noted "a frustration that began to ferment" amongst the delegates. In the 1954 election, that frustration led to a huge victory for the Democrats, who seized control of what had been a territory dominated by Republicans. Doi, representing Hawaii Island, was one of the victorious Democrats. Other Democrats first elected in 1954 included U.S. Senator Dan Inouye, former Governor George Ariyoshi, the late U.S. Senator Spark Matsunaga.