Tributes have since flooded in for Sir Harold with campaigners, fellow journalists and politicians among those sending condolences to his family.
Ms Brown wrote on Twitter that Sir Harold was "the most magical of men".
“I lost the love of my life last night, my darling Harry," she wrote “He was peaceful at home with his family. My soulmate for 39 years.
“Thank you for all the beautiful tributes to the most magical of men.”
Among those paying homage were the victims of the thalidomide scandal, which Sir Harold helped to expose.
Glen Harrison, a thalidomide survivor and deputy chairman of the campaign group Thalidomide UK, described him as a “true warrior, a true champion for our cause”.
Sir Harold, who was also editor-at-large for the Reuters news agency, died of congestive heart failure, according to Ms Brown.
Born into a working-class family in Manchester in 1928, Harold Evans began his career at a weekly newspaper in Ashton-under-Lyne aged 16.
He rose through the newspaper industry with roles including assistant editor of the Manchester Evening News and, after a stint in the US, editor of The Northern Echo in Darlington.
I lost the love of my life last night, my darling Harry. He was peaceful at home with his family. My soulmate for 39 years. Thank you for all the beautiful tributes to the most magical of men. @sirharryevans pic.twitter.com/uZk6v745ZP— Tina Brown (@TinaBrownLM)September 24, 2020
Peter Barron, Northern Echo editor from 1999 to 2016, paid tribute to his predecessor, saying: “I was editor half a century later and the people of County Durham, North Yorkshire and Darlington still revered him.
“If I went to give a talk in the community, Harold Evans always came up, at Women’s Institutes, Townswomen’s Guilds and Rotary Clubs, somebody always had a memory of him.
“He made a lasting impression on the people of the North East because of his journalism.
“He changed the world, he believed in campaigning journalism and he also understood the importance of getting out and listening to people.”
Sir Harold, who received a knighthood in 2004, became editor of The Sunday Times (ST) in the late 1960s and editor of The Times soon after Rupert Murdoch bought the paper in 1981. He left around a year later after clashing with Mr Murdoch over editorial independence.
Sir Harold was renowned for his promotion of investigative journalism.
His most famous investigation involved thalidomide, a drug prescribed to expectant mothers for morning sickness which caused many thousands across the world to give birth to children with missing limbs, deformed hearts, blindness and other problems.
Sir Harold fought off a legal attempt by UK manufacturer Distillers – a major Sunday Times advertiser at the time – to stop the paper revealing that the drug’s developers had not gone through proper testing procedures.
And his campaign, launched in 1972, forced Distillers to increase the compensation received by victims.
Mr Harrison said: “He was an outstanding human being for our cause.
“A true gentleman and honestly we wouldn’t know where we would be without him, a really sincere loss and condolences to his family.”
Another thalidomide campaigner, Guy Tweedy, from Harrogate, also mourned the passing of a “dear friend”.
“He was an icon. The world’s greatest journalist and Harry was, and will always remain, a hero of thalidomiders worldwide.
“What he did for thalidomide survivors and their families in the UK was enormous. He trod where no one else did.
“If it wasn’t for him fighting against the establishment, and having the courage to expose this horrendous scandal, we would never have got any justice at all.”
Sir Harold described journalism as his “basic passion” and was a firm advocate for accurate, truthful reporting.
He was also conscious of the power of journalism and the media, saying: “The camera cannot lie, but it can be an accessory to untruth.”
On his investigations, he once said: “I tried to do – all I hoped to do – was to shed a little light. And if that light grew weeds, we’d have to try and pull them up.”
Culture Secretary Oliver Dowden said the death of Sir Harold “should remind us of the vital role the free press plays in our democracy”.
“He was a giant of investigative journalism, uncovering great injustices and informing the public without fear or favour,” he said.
“At a time our newspapers remain under serious pressure, we can all help #buyapaper.”
Boris Johnson, a former journalist at the Times who was dismissed for inventing a quote, said: “Sir Harold Evans worked his way up from local papers to become a giant of British journalism.
“He will always be remembered for exposing the thalidomide scandal and for tirelessly campaigning on behalf of those who were affected.
“A true pioneer of investigative journalism.”