Researchers say that the letter - which required state of the art imaging techniques to decipher - helps round out the picture of a man traditionally cast as an intrepid Victorian hero, revealing the self-doubt that tormented the missionary-explorer in one of his darkest hours.
"I am terribly knocked up but this is for your own eye only," Livingstone wrote to close friend Horace Waller in the newly revealed correspondence. "Doubtful if I live to see you again."
Livingstone was a national hero when he set off to find the source of the River Nile in 1866, but by the time he composed his four-page missive he was at the lowest point in his professional life, according to Debbie Harrison, a researcher at Birkbeck University of London.
The explorer was stuck in the village of Bambarre, in present-day Congo, in February of 1871. He was a long way off from his intended goal, most of his expedition either died or deserted him, and he was still suffering the effects of pneumonia, fever, and tropical eating ulcers - a nasty condition that consumes skin and flesh.
Adding insult to injury, Livingstone, a crusading abolitionist, had been forced to seek help from Arab slave traders while he waited for outside support. Bedridden for weeks on end, Livingstone had read the Bible several times over and started hallucinating.
"He'd gone slightly mad by this point, to be honest," Harrison said.
Back home, Livingstone's supporters were going mad with worry. No one had heard from him in years, and as Livingstone recovered, search parties set out into the interior to discover his fate. He was eventually located near the eastern shore of the massive Lake Tanganyika by journalist Henry Morton Stanley, whose memorable quip, "Dr. Livingstone, I presume?" immortalized their encounter.
But Livingstone refused to leave Africa, continuing his obsessive quest for the source of the continent's longest river. His warning to Waller was prescient: He finally succumbed to illness in May 1873, at Chitambo in what is now Zambia.
It's not clear how Livingstone's letter ever left the continent, although presumably Stanley took it back to Waller. The document disappeared from view for nearly a century before surfacing again at auction in 1966.
By then it was indecipherable. Out of paper and low on ink, Livingstone tore pages from books and newspapers and wrote with a pigment improvised from the seeds of a local berry. A century later, the makeshift ink had nearly faded to invisibility, a problem compounded by the brittle paper and Livingstone's chaotic handwriting.
A team of scientists and academics - including spectral imaging specialists from the United States - analyzed the fragile paper, carefully drawing out Livingstone's original text.
The university said the newly revealed letter projects an image at odds with the fearless hero depicted by Waller, who heavily sanitized Livingstone's writings before they were published posthumously.
"It's an opportunity to rewrite history," said Harrison of Birkbeck, which announced the find. "It's giving us a new way of looking at Livingstone. He got depressed, he did think he'd failed at times. But he never gave up ... It makes him human."
Harrison said that while the explorer was "very politically incorrect in his writings and his ramblings," his friend was "very concerned to maintain that image of Livingstone as a saintly martyr and to suppress anything that might have offended Victorians."
The letter published Friday is part of an 18-month project to produce a new - and unvarnished - edition of the diary Livingstone kept between 1870 and 1871.