Valerie Mahaffey, a character actress with a knack for playing eccentric women who sometimes revealed themselves to be sinister on television shows like “Desperate Housewives,” “Northern Exposure” and “Devious Maids,” died on Friday in Los Angeles. She was 71.

The cause was cancer, her husband, the actor Joseph Kell, said in a statement.

Ms. Mahaffey had worked steadily over the past five decades. Her first significant role was on the NBC daytime soap opera “The Doctors,” for which she received a Daytime Emmy nomination for best supporting actress in 1980. She was seen most recently in the movie “The 8th Day,” a crime thriller released in March.

She was also known for her guest-starring roles on prominent TV series, including “Seinfeld” — on which she memorably played an accountant who is dating Jerry’s friend George Costanza and offers to help Jerry with his taxes — and “Grey’s Anatomy.”

She won an Emmy for best supporting actress in 1992 for her work as Eve, a hypochondriac, on the “Northern Exposure,” the CBS comedy-drama about a New York doctor who moves to a small town in Alaska.

Ms. Mahaffey was best known for playing seemingly friendly women who become villainous on dramas like “Desperate Housewives,” where she appeared in nine episodes. Her character, Alma Hodge, was a woman trapped in a loveless marriage who faked her own death to get back at her husband, hoping that he would be blamed for her disappearance.