He was tax commissioner of North Dakota from 1969 until 1980, when he was elected to the United States House of Representatives, of which he was a member from 1981 until 1992, being reelected every two years. In 1992 he ran for the Senate when the Democratic incumbent, Kent Conrad did not run. Dorgan won the election. He took office a few weeks early, in December 1992, when the governor appointed him to fill the rest of the term of Conrad, who had won a special election to fill the rest of the term of a deceased senator. Dorgan was reelected in 1998.