The book, serialised in The Times, will claim that Harry felt "unprotected" by his family, and lay bare his split from brother William and his wife Kate.
Kate even refused to make eye contact with her sister-in-law at their final engagement in March, according to the new release.
Harry apparently referred to senior courtiers as "vipers" who felt that the global popularity of the couple was overshadowing the family and "needed to be reined in", according to extracts.
The book, to be released on August 11, also suggested that Harry, 35, was the driving force behind the couple's move away from the family, with Meghan telling her husband that she "gave up my entire life for this family".
The couple now live in Los Angeles and were in the headlines this week for taking legal action against one or more paparazzi whom they accuse of taking pictures of their son Archie without permission.
Pressure from tabloids has dogged Harry throughout his life, and he blames them for the death of his mother Princess Diana.