Harry, 36, said his memoir would be a "first-hand account" of his life so far and the prince would touch on the "mistakes" he has made and the "lessons" he has learned.
In a statement, he said: "I'm writing this not as the prince I was born but as the man I have become.
"I've worn many hats over the years, both literally and figuratively, and my hope 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.
"I'm deeply grateful for the opportunity to share what I've learned over the course of my life so far and excited for people to read a first-hand account of my life that's accurate and wholly truthful."
The duke has been writing the book alongside ghost-writer JR Moehringer. The memoir does not yet have a name.
A blurb from the publisher stated: "In an intimate and heartfelt memoir from one of the most fascinating and influential global figures of our time, Prince Harry will share, for the very first time, the definitive account of the experiences, adventures, losses, and life lessons that have helped shape him."
The description went on to say Harry's book would cover his "lifetime in the public eye", as well as "the joy he has found in being a husband and father".