A few years ago I was researching a book about Einstein when I stumbled on a footnote about an obscure Frenchwoman of the early 18th century. Her name was Emilie du Châtelet; according to the note, she had played a role in developing the modern concept of energy, and had acquired a certain notoriety in her day.

It left me intrigued. And what I discovered, as I tracked down her letters and books over the next few months, astounded me. That footnote had understated her significance entirely. Emilie du Châtelet had played a crucial role in the development of science. What's more, she had had a wild life.

She had been raised in Paris in the 1710s, growing up in a townhouse of more than 30 rooms overlooking the Tuileries gardens. Her mother had been appalled at having a child who refused to stay politely at children's parties, or to gossip about clothes, but who instead loved listening in when educated guests - especially astronomers - came to visit.

Du Châtelet's father, luckily, doted on his sole daughter. He kept the mother from sending her off to a convent, as was regularly threatened; he hired tutors to teach her Latin, Greek and mathematics. At Versailles, where her black curly hair and rapid-fire speech won her admirers, he merely sighed when she used her skill at mathematics to win at cards, and then used the money to buy more books, rather than more clothes. But he helped her, with family money, to arrange a marriage with a wealthy army officer who - luckily - would be away with his regiment most of the time.

In her late 20s, after an affair with the individual who inspired the character Valmont in Les Liaisons Dangereuses (she was the only partner he had who ever willingly dumped him), she met the poet and writer Voltaire, then in his 40s. He was delighted with her youth and intelligence:

Why did you only reach me so late?

What happened to my life before?

I'd hunted for love, but found only mirages.

She teased him for that, but was thankful that she had finally found someone with whom she could let her intelligence pour forth.

Together she and Voltaire created something of a modern research institute in an isolated chateau they had rebuilt in eastern France. The chateau was like a berthed spaceship from the future. Visitors from intellectual centres in Italy and Basle and Paris came to scoff, then stayed, and became awed by what they saw.

I found accounts of Du Châtelet and Voltaire at breakfast, reading from the letters they received - from the mathematician Bernoulli, and Frederick the Great of Prussia (earlier there had been correspondence with Bolingbroke and Jonathan Swift) - and in their quick teasing at what they heard, coming up with fresh ideas. Then they returned to their separate wings of the house and competed to elaborate.

This is where the great problem with her subsequent reputation began, for Voltaire wasn't much of a scientist, but Du Châtelet was a skilled theoretician. Once, working secretly at night at the chateau over just one intense summer month, hushing servants to not spoil the surprise for Voltaire, she came up with insights on the nature of light that set the stage for the future discovery of photography, as well as of infrared radiation. It was a humiliating contrast for Voltaire, and especially grating when she began to probe into the still recent mathematical physics of Sir Isaac Newton.

Voltaire could not follow any of the maths, but on political grounds he wanted to believe that Newton was perfect in all respects. Du Châtelet, however, began a research programme that went beyond Newton and led to her glimpsing notions that would lead later researchers to the idea of conservation of energy fundamental to all subsequent physics.

For that, and other reasons, she and Voltaire broke up: he was immensely proud, and couldn't bear to have as a lover someone who could so clearly see his weaknesses.

Now though, in the early 1740s, while Voltaire was in his imperious sulk, she tried to insist that she would be fine without him; indeed, she wrote that it was preposterous to think that an intelligent woman needed a man to be happy.

And then, when she was 41 - in 1748 - she met a fit young poet at a provincial court, and fell in love with him. At first he loved her back, but then he got scared, for he knew he couldn't keep up with her or her sophisticated friends. He became cruel to her, and got her pregnant.

At that time it was a death sentence to be pregnant in one's 40s. Voltaire went back, out of friendship, to support Du Châtelet. She had always worked at night, but now began staying up later and later to finish the manuscript on Newton that she hoped might be her claim to immortality. Voltaire wrote that she wasn't angry, just sad to have to leave before she was ready. She finished her text at the end of August, 1749, a few days later she gave birth, and within a week she - and the child - were dead.

Almost immediately after Du Châtelet's death, sharp-tongued gossips began to disparage her work. Then, as her insights entered the scientific mainstream, the idea that a woman had created these thoughts was considered so odd that even scientists who did use her ideas came to forget who had originated them.

In the late 1930s, better scholarship brought at least some of her achievements back to life, but in 1957 Nancy Mitford wrote a biography of Voltaire that set historians on the wrong path again: it painted Du Châtelet as a cut-out character who had dashing adventures, but for no discernible reasons.

Emilie du Châtelet deserves to be brought back to life, in all her stumbling excitement and fears.

David Bodanis is the author of Passionate Minds: The Great Enlightenment Love Affair, published by Little, Brown