Jean Marsh, the striking British-born actress who was both the co-creator and a beloved Emmy-winning star of “Upstairs, Downstairs,” the seminal 1970s British drama series about class in Edwardian England, died on Sunday at her home in London. She was 90.

The cause was complications of dementia, the filmmaker Michael Lindsay-Hogg, her close friend, said.

“Upstairs, Downstairs” captured the hearts, minds and Sunday nights of Anglophile PBS viewers decades before “Downton Abbey” was even a gleam in Julian Fellowes’s eye.

The show, which ran from 1971 to 1975 in England and from 1974 to 1977 in the United States, focused on the elegant Bellamy family and the staff of servants who kept their Belgravia townhouse running smoothly, according to the precise social standards of Edwardian aristocracy. Ms. Marsh chose the role of Rose, the household’s head parlor maid, a stern but good-hearted Cockney.

The New York Times review, in January 1974, was affectionate. John J. O’Connor described the show as “a charmingly seductive concoction” and a “frequently marvelous portrait.” He praised Ms. Marsh for playing Rose with “the perfection of a young Mildred Dunnock.”

By the time the show ended its American run, it had won a Peabody Award and seven Emmys. Ms. Marsh herself took home the 1975 Emmy for outstanding lead actress in a drama series.