The Duke and Duchess of Sussex filed suit against the Daily Mail's parent company after the tabloid published a private letter written by Meghan Markle earlier this year.
The royal couple filed a claim against Associated Papers for the misuse of private information, infringement of copyright and breach of the United Kingdom's Data Protection Act 2018, according to the law firm representing the couple.
Harry also penned a scathing statement against the British tabloids for a "ruthless campaign" against his wife.
"I’ve seen what happens when someone I love is commoditized to the point that they are no longer treated or seen as a real person," he said. "I lost my mother and now I watch my wife falling victim to the same powerful forces."
Harry's mother, Princess Diana, died in a 1997 car accident while trying to escape paparazzi in Paris.
Harry accused the Mail of publishing a private letter from his wife "in an intentionally destructive manner" by editing out entire paragraphs to manipulate readers.
"There is a human cost to this relentless propaganda, specifically when it is knowingly false and malicious, and though we have continued to put on a brave face – as so many of you can relate to – I cannot begin to describe how painful it has been," Harry said.
Though the couple did not name the exact letter in their statement, the Mail on Sunday published a handwritten letter from Markle to her estranged father, Thomas Markle, in February.
"The Mail on Sunday stands by the story it published and will be defending this case vigorously. Specifically, we categorically deny that the Duchess’s letter was edited in any way that changed its meaning," a spokesman for the paper said.
British tabloids have intensely scrutinized the duchess, publishing stories about her estranged family following her engagement to Prince Harry and more recently attacking her for guest-editing an issue of British Vogue.
Singer Elton John defended the couple in August after The Sun criticized them over the use of a private jet to travel with their young son, Archie, despite their dedication to environmental causes.
John said he and his partner, David Furnish, provided the jet because they "wanted the young family to have a private holiday" inside the safety and tranquility of the singer's home.
"I feel a profound sense of obligation to protect Harry and his family from the unnecessary press intrusion that contributed to Diana’s untimely death," John said.
The 72-year-old singer also said that he donated to a fund that offsets carbon emissions to ensure the flight was carbon neutral.