Six years after former National Security Agency (NSA) contractor Edward Snowden leaked a secret government programme to track every phone call and text being made, the American whistleblower has announced that his memoir will be released on Constitution Day, September 17.

In a video posted on Twitter, Snowden outlined the theme of Permanent Record, which will be about the mass surveillance program that he helped build with the NSA.

"Everything that we do now lasts forever. Not because we want to remember. But, because we're no longer allowed to forget. Helping to create that system is my greatest regret."

I wrote a book. pic.twitter.com/wEdlOFMnMn — Edward Snowden (@Snowden) August 1, 2019

The book will be published by Macmillan, whose website says that "The book will tell the story of his time working as a CIA agent and NSA contractor, and the disillusionment he felt with the American intelligence establishment that led him to give up his future to share the truth about the US government’s pursuit of a mass surveillance system."

Snowden was charged with violating the Espionage Act of 1917 by revealing classified information, and of stealing government property for leaking parts of the 1.7 million government documents he is believed to have accessed.

Snowden's last book, Everything you know about the Constitution is wrong, was published in 2013.