McIntyre, a nine-term member of the House, said in a statement posted on his official website he tried to put "policy over politics, issues over ideology, dialogue over dollars and cooperation over campaigning."
Among other things, he cited as accomplishments "quadrupling the number of veterans' clinics in our area, passing the tobacco buyout, expanding our military bases, establishing an economic commission to promote jobs and fight poverty -- and ensuring that the North Carolina coast will continue to be an economic engine and environmental treasure."
Washington publications Roll Call and the Hill cited sources as saying McCarthy, who disclosed last June she has lung cancer, would not seek a 10th term.
McIntyre was expected to face another strong challenge from Republicans, while McCarthy's seat is seen as more likely to remain in the Democratic fold.
Roll Call notes a dozen members of the House -- three Democrats and nine Republicans -- and seven senators -- five Democrats and two Republicans -- have announced they will retire at years' end.