Inouye was born in Hawaii and spent his childhood there. He was in the United States military from 1943 until 1947, and experienced combat during the later stages of World War II. When he retired he was a captain. He went to college, and by 1953 he had become a lawyer. Soon afterward he was elected to the territorial legislature, of which he was a member until shortly before Hawaii achieved statehood in 1959. He won a seat in the United States House of Representatives as one of Hawaii's first full members, and took office on August 21, 1959, when Hawaii became a state. He was reelected in 1960.
In 1962 he was elected to the United States senate. He has been reelected every six years; 1968, 1974, 1980, 1986, 1992 and 1998. He was chairman of the Select Committee on Intelligence from 1975 until 1979, and chairman of the Committee on Indian Affairs from 1987 until 1995 and from 2001 until 2003. Inouye was also involved in the Iran Contra investigations of the 1980s, chairing a special committee from 1987 until 1989.