Since her death in 1977, Lee Miller has emerged as one of the most extraordinary photographers of the 20th century. This recognition is largely due to her son, Antony Penrose, who discovered thousands of negatives, prints and documents packed away in the attic of his parents' Sussex farmhouse. Penrose, who had been estranged from his mother for much of his life, set about resurrecting the reputation of a woman once acclaimed for her penetrating celebrity portraits and whose legendary beauty and hedonistic free spirit set her at the heart of European cultural life between the wars. The stunning exhibitions at the Scottish National Gallery of Modern Art in Edinburgh in 2001 and at the National Portrait Gallery in London this year confirmed that reputation, not least because Miller's life was as remarkable as her work.

Penrose's The Lives of Lee Miller (1985) went some way towards explaining his mother's uncon- ventional world, but now Carolyn Burke's searching biography attempts to fill in the gaps, analysing Miller through her work. She succeeds for the most part, though inevitably an element of inscrutability remains. What is indisputable is that while Miller's life was a series of transformations, her metamorphosis from Vogue fashion model to combat photojournalist was the most singular journey of all.

Born in 1907 in Poughkeepsie, New York State to indulgent, progressive parents, Miller had a steely instinct for survival that may have become ingrained early on. Her engineer father, Theodore, was a keen amateur photographer whose favourite subject was his nude daughter. Miller happily modelled for him well into her twenties, and they remained close until he died. Shockingly, at the age of seven, she had been raped by the nephew of a family friend and infected with gonorrhoea. The psychic scars left by this trauma undoubtedly shaped the complex sexual and emotional landscape of her adult life. She became promiscuous and defiant, and although she always had a great need for love she refused to be confined by it.

In 1929, bored with modelling and determined to become a photographer, she left New York for Paris to apprentice herself to the surrealist artist-photographer Man Ray. Ray taught her everything he knew, and for three years she was his assistant, muse and lover. She was soon taking on both portrait and fashion assignments for French Vogue (or Frogue, as it was known) and running her own studio.

In 1932 she left a heartbroken Man Ray to open an equally successful studio in New York, but after two years married a wealthy Egyptian businessman, Aziz Eloui Bey, and went to live in Cairo. Homesick for Paris, she returned there in summer 1939 and began an affair with the English surrealist painter and collector Roland Penrose, moving with him to London at the outbreak of the Second World War. She worked for British Vogue, but found as the war progressed that she wanted to be part of it. In 1942 she was granted accreditation with the US army as a war correspondent, having persuaded Vogue to publish her stories. Teamed with David Scherman - the Life photographer and a fellow New Yorker (who also formed a menage a trois with Miller and Penrose in their Hampstead home) - she spent the defining, and happiest, years of her life. With the Allies, she witnessed the siege of St Malo and the liberation of Paris, and was among the first to enter Dachau and Buchenwald and photograph their horror. In Munich, she took a bath in Hitler's abandoned apartment - one of the century's great photographic scoops - and on the eve of Germany's surrender she watched the burning of his mountain retreat at Berchtesgaden.

Following the armistice, Miller ("encased in a wall of hate and disgust") wandered eastern Europe recording the tragic fallout of war, reluctant to return home. "Lee came into her own during the war," said her Vogue editor, Audrey Withers. "It had an extraordinary effect on her. Afterwards, nothing came up to it."

In 1947, when she was 40, she married Penrose and later that year gave birth to her only son. In 1949, they bought Farley Farm in East Sussex, which became a magnet for artist friends such as Picasso, Miro and Max Ernst. Miller's displacement activities included entertaining, travelling, gourmet cookery, classical music and, to the detriment of her looks and personality, drinking heavily. She existed, David Hare says, in a kind of "rural rage", but the past remained a closed door.

In a chance encounter shortly before Miller's death, Carolyn Burke met her in Paris. Surprisingly, she records very little of their conversation, except to say that when they touched upon the subject of war, Miller confessed: "I got in over my head. I could never get the stench of Dachau out of my nostrils." By that time she had already been diagnosed with cancer, but at 70 had lost none of the fearless curiosity that fuelled so much of her life. "She was the nearest thing I knew to a mid-20th-century Renaissance woman," Scherman said affectionately of his ex-lover and compadre. "She was a mensch."