Inouye, a World War II veteran who was first elected to the Senate in 1962, was declared the winner with 76 percent of the voter by CNN.
Inouye is the chairman of the powerful Senate Appropriations Committee and senior Democrat on the Commerce Committee, which oversees a mixed bag of business interests including telecommunications, the Internet and air travel.
Votes for two House districts were still being tallied, but incumbent Democrat Mazie Hirono had a wide lead in the 2nd District. First District Republican incumbent Charles Djou, who just took office in May after Democrat Neil Abercrombie stepped down to run for governor, was trailing Democratic challenger Colleen Hanabusa.
Abercrombie had opened up a comfortable lead in the gubernatorial race.