"Thirty-eight years. 38 years of having my story told by so many different people with intentional spin and distortion felt like a good time to own my story and be able to tell it for myself," he told British channel ITV in an interview broadcast on Sunday.
The Duke of Sussex's ghost-written book "Spare" is officially published on Tuesday, but its contents were widely leaked after it mistakenly went on sale early in Spain.
The book includes a claim that his brother Prince William, the heir to the throne, physically attacked him as they argued about Harry's wife Meghan.
It also gives an account of how he lost his virginity, an admission of drug use, and a claim that he killed 25 people while serving in Afghanistan with the British military.
In the TV interview, Harry focused anger on the British media, which he called "the antagonist".
He accused royals of being "complicit" in planting hostile stories in newspapers, after Meghan said the coverage made her feel suicidal.
"Certainly millions of words have been dedicated to trying to trash my wife and myself," Harry said.
"At that time I didn't fully understand how complicit the family were in the pain and suffering that was happening to my wife."
The ITV programme "Harry: The Interview" featured the prince reading extracts from the audiobook of his memoirs.
In one, he tells how his father broke the news to him of the 1997 death of his mother, princess Diana, calling him "darling boy".
Harry said he cried only once after Diana died, and he felt guilty at being unable to express grief while greeting crowds of mourners whose hands were wet with tears.
He also talked about later going to see the route Diana's car took before the crash, asking a driver to take him through the road tunnel in Paris at the same speed.
"I've been asked if I want to open up another inquiry," Harry said of Diana's death.
"I don't really see the point at this stage."
But he admitted he had lingering questions.
The book focuses on his combative relationship with William. Harry says his elder brother physically attacked him as they argued over Meghan.
"I saw this red mist in him," Harry told ITV. "I want reconciliation, but first there has to be accountability."
The prince said his budding relationship with Meghan triggered a falling-out with William and his wife Kate.
He denied reports the couples initially got on well, saying the newspapers' nickname of "the Fab Four" for them "was something that the British press created".
The prince also criticises Charles's second wife Camilla in the book.
He writes that after Diana's death, Camilla "began playing the long game: a campaign aimed at marriage and eventually the crown".
Details appeared in media of private conversations that "could only have been leaked" by Camilla, Harry alleged.
"I love my father, I love my brother, I love my family," Harry said in the CBS interview.
Harry added that he and William were not currently on speaking terms and that he hadn't talked to his father "for quite a while."