Veteran political campaigner John Catt, from Brighton, has won a Court of Appeal challenge in his battle to have details about his attendance at various protests removed from a police "extremism" database.
He argued that as he has not engaged in any criminality, the retention of data about him on the National Domestic Extremism Database was unlawful.
Last year, Mr Catt - who said his human rights were being violated - urged two judges at the High Court in London to order the removal of details about his activities from the database, which is operated by police chiefs.
But Lord Justice Gross and Mr Justice Irwin dismissed his judicial review claim, ruling that his right to privacy under Article 8 of the European Convention on Human Rights was not infringed.
Today, following a hearing at the Court of Appeal in January, Master of the Rolls Lord Dyson, Lord Justice Moore-Bick and Lord Justice McCombe, announced that they had allowed Mr Catt's appeal against that earlier decision.
They said they had reached the conclusion that the "interference with Mr Catt's right to respect for his private life has not been justified and that the appeal must therefore be allowed".
Mr Catt said in a statement: "I hope this judgment will bring an end to the abusive and intimidatory monitoring of peaceful protesters by police forces nationwide. Police surveillance of this kind only serves to undermine our democracy and deter lawful protest."