She is said to be the main influence behind recent efforts to present the 'Iron Chancellor' in a softer, more human light.
But Sarah Brown is expected to be a far lower-profile 'First Lady' than Cherie Blair when her husband finally gets the job he has craved for so long.

While Mrs Blair has pursued a high-flying career while in Downing Street and has often been at the centre of controversy, Mrs Brown is likely to shun the limelight and offer her counsel behind closed doors.

Born to a teacher mother and Scottish publisher father in Buckinghamshire in October 1963, Sarah Macaulay had a comfortable - if not always conventional - upbringing.

A portion of her early years were spent in Tanzania, and Mr Brown made a point of calling at her old school during a visit to the African state in 2004.

However, Mrs Brown's parents reportedly separated when she was seven, and she settled in north London with her mother.
After gaining a degree in psychology from Bristol University, Mrs Brown joined public relations agency Wolff Olins, and began developing strong links with the left's movers and shakers.

Aged barely 30, she struck out with schoolfriend Julia Hobsbawm by forming their own PR firm, Hobsbawm Macaulay, which represented unions and the Labour party.

She became friends with Mr Brown's then-spin doctor Charlie Whelan and influential political adviser Sue Nye, and in the mid-1990s also got to know the future Chancellor himself.

Their relationship is thought to have begun at around this time, but was not acknowledged publicly until 1997, when Whelan invited the News of the World to photograph them having dinner together.

The photo reputedly had to be re-shot because the notoriously grumpy Chancellor did not look sufficiently adoring.

The pair were married in August 2000 in a private ceremony at Mr Brown's home in Queensferry, Fife.

Mrs Brown took her husband's name, and cut all ties with her PR company as she abandoned her successful career in preparation for life under the public microscope.

Since then she has restricted her professional activities to charitable work - much of which has been inspired by the couple's personal struggles.

In 2002 their first child, Jennifer Jane, died aged just 10 days. The experience led the Browns to start the Jennifer Jane Research Fund to investigate the causes of premature births.

It was disclosed in November last year that the couple's younger son, Fraser, had been diagnosed with cystic fibrosis, and they have been involved in fundraising for research into the condition.

Mrs Brown has also acted as patron for Women's Aid and Maggie's Cancer Caring Centre, among other causes.