Associated Newspapers Limited (ANL) had attempted to overturn the High Court judge's decision not to go to trial. The Court of Appeal said it is "hard to see what evidence could have been adduced at trial that would have altered the situation," per Sky News.
The 40-year-old sued ANL after five articles published in February 2019 included parts of the letter.
"This is a victory not just for me, but for anyone who has ever felt scared to stand up for what's right," the Duchess of Sussex said in a statement. "While this win is precedent-setting, what matters most is that we are now collectively brave enough to reshape a tabloid industry that conditions people to be cruel, and profits from the lies and pain that they create."
Markle said that she always treated the lawsuit as an "important measure of right versus wrong" while the defendant "treated it as a game with no rules."
"The longer they dragged it out, the more they could twist facts and manipulate the public (even during the appeal itself), making a straightforward case extraordinarily convoluted in order to generate more headlines and sell more newspapers — a model that rewards chaos above truth," the Suits alum stated.
"In the nearly three years since this began, I have been patient in the face of deception, intimidation, and calculated attacks," she continued. "As far removed as it may seem from your personal life, it's not. Tomorrow it could be you. These harmful practices don't happen once in a blue moon — they are a daily fail that divide us, and we all deserve better."
During the appeal hearing, ANL claimed that Markle wrote the letter with the knowledge it could be leaked. Markle said that she "recognised that this was a possibility" but denied that she thought it was likely her father would leak the letter in her written evidence.
The court upheld the ruling that Markle has a "reasonable expectation of privacy in the contents of the letter." "These contents were personal, private, and not matters of legitimate public interest," the judgment read.
"The judge had been in as good a position as any trial judge to look at the article in People magazine, the letter and The Mail On Sunday articles to decide if publication of the contents of the letter was appropriate to rebut the allegations against Mr Markle," the court said. "The judge had correctly decided that, whilst it might have been proportionate to publish a very small part of the letter for that purpose, it was not necessary to publish half the contents of the letter as ANL had done."