The Duke of Sussex will share "mistakes and lessons learned" during his life in a memoir to be published next year.
Announcing SLOTXO the deal with publishers Penguin Random House, Prince Harry said he would reflect "the highs and lows" and be "accurate and wholly truthful".
Harry, who alongside his wife Meghan stepped back from royal duties last year, will donate proceeds to charity.
The BBC has been told the duke has recently spoken privately with his family about writing the book.
A spokesperson for the duke added that he would not be expected to obtain permission for the project from Buckingham Palace.
They did not provide additional details on what share of the proceeds would be donated to charity.
And Penguin did not disclose the terms of its deal, which includes an audio book and international rights.
The duke, 36, said in a statement: "I'm writing this not as the prince I was born but as the man I have become."
He added: "I've worn many hats over the years, both literally and figuratively, and my hope is that in telling my story - the highs and lows, the mistakes, the lessons learned - I can help show that no matter where we come from, we have more in common than we think.
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