Ms MacCarthy was the widow of the noted Sheffield cutlery designer, David Mellor, whom she met when assigned by The Guardian in 1964 to write about his Pride range of fashionable knives and forks and his work in redesigning Britain’s traffic light system.
She profiled him at his studio and bedsit on Park Lane, Broomhall, and they married two years later, moving eventually into the elegant Broom Hall after which the district is named.
She inspired the launch of the first David Mellor shop in London’s Sloane Square, but it was the circular factory he and she created in Sheffield that was to be their lasting legacy. The distinctive Round Building, on a five-acre site just outside Hathersage, was where the family’s kitchenware products were turned out and also Ms MacCarthy’s base as a writer.
Her links to Sheffield’s traditional metalwork industries had inspired her to write her first book, on the architect and designer Charles Robert Ashbee, in 1981. The biography of Gill, the controversial sculptor and typeface designer, followed in 1989.
She also wrote biographies of the designer William Morris, the artist Stanley Spencer and the poet, Lord Byron. Her final work, published last year, profiled Walter Gropius, founder of the Bauhaus art school.
The great-granddaughter of the engineering contractor Sir Robert McAlpine, she lost her father when she was still an infant. Gerald MacCarthy, a Royal Artillery officer, was killed in action in North Africa. She and her baby sister grew up in London and Scotland and Fiona studied at Oxford. In 1958, following time at a Paris finishing school, she was one of the last young debutantes to officially “come out” into society.
Possessing an eye for good design, she progressed to a job at House and Garden magazine, and was for a short time the women’s editor of the Evening Standard. At The Guardian, where she was ostensibly the design reporter, her profiles of Lennon, Hockney and others earned her the epithet “swinging 60s correspondent”.
In later life, she curated exhibitions for the V&A, Museums Sheffield and the National Portrait Gallery, and was appointed OBE in 2009, for services to literature. She served as president of the 20th Century Society, and was a fellow of the Royal College of Art and the Royal Society of Literature.
Widowed in 2009, she is survived by her children, Clare and Corin, both of whom are designers.