Benn twice tested positive for the fertility drug clomifene -- which elevates testosterone levels in men.
Those findings led to his scheduled grudge contest with British rival Chris Eubank Jr at London's O2 Arena on Oct. 8, 2022 to be called off.
Benn had his license removed by the British Boxing Board of Control, and although his provisional suspension was lifted by the NADP in July 2023, it was subsequently reinstated after a successful appeal by the Board and the U.K. Anti-Doping Agency (UKAD).
But the NADP has now reversed that decision saying it was "not comfortably satisfied" UKAD had proved Benn had committed a doping offense.
The 28-year-old responded to the latest development in his case in a social media post.
"I am thankful that after an incredibly challenging two years the National Anti-Doping Panel has today finally cleared me of any wrongdoing," said Benn, who has fought twice in the United States since his provisional ban was lifted.
"This past 24 months has unquestionably been the toughest fight of my life. As someone who is so passionate about boxing and an advocate for clean sport, I hope now I have been cleared it can be understood why I have maintained my innocence so strongly throughout."
UKAD said it would "carefully review" the NADP ruling before deciding on whether to lodge a further appeal.
The proposed 2022 bout was intended to be a continuation of the Benn v Eubank rivalry in which the boxers' fathers -- Nigel Benn and Chris Eubank Sr -- battled it out in two ferocious contests in the early 1990s.