Alexandra Shulman, the longest-serving editor-in-chief of fashion magazine British Vogue, has announced she is stepping down after 25 years in the role.

Nicholas Coleridge, the managing director of Condé Nast Britain, said: "This is an announcement I hoped never to have to make. Alexandra Shulman, Editor-in-Chief of British Vogue for a quarter of a century, told me before Christmas that she had decided to stand down from Vogue in six months time."

"Alex has been the longest serving and most successful Editor of Vogue in its 100 year history. She has edited the title for a quarter of its existence, through its period of highest ever circulation, and its simultaneous transformation into a global digital brand."

"She has been the towering figure of the British fashion press throughout her tenure: a superb journalist and editor, who understands and exemplifies every quality. Imaginative, hard-working, perceptive and a brilliant leader, Alex is also a valued friend to so many of us."

"It is impossible to sufficiently express the contribution she has made to Vogue, to Condé Nast and to the British fashion industry."

On her departure from the magazine, Shulman said: "I have edited British Vogue for 25 years almost to the day, and to have steered it during our spectacular centenary has been one of the greatest privileges. During that time I have worked with an unparalleled collection of talent both inside and outside the magazine and have been lucky enough to see both Vogue and the British fashion industry expand and flourish."

"It has been very hard to find a rational reason to leave what is unquestionably a fascinating and rewarding role but last autumn I realised that I very much wanted to experience a different life and look forward to a future separate to Vogue."

Shulman was born into a family of journalists as the daughter of Drusilla Beyfus, a Vogue contributor, and Milton Shulman, a film and literary critic. She began her fashion journalism career in 1982 at Tatler, before taking the position of features editor at the magazine. In 1987, she began working at the Sunday Telegraph.

She joined British Vogue as features editor in 1988, before moving to GQ as editor in 1990. She then returned to Vogue in 1992.

Some of Shulman's most notable issues of the magazine include a 1997 cover in memoriam of Princess Diana, and a 'heroin chic' cover featuring Kate Moss in the early 1990s – which critics accused of promoting anorexia.