A food writer has won £24,000 in damages in a libel suit against columnist Katie Hopkins over two tweets.
Blogger Jack Monroe sued Hopkins over the tweets that implied she defaced or condoned the damage to a war memorial in central London.
Former Apprentice star Hopkins, who was not present at court during the trial, has also been ordered to pay £107,000 costs within the next month, with the full figure yet to be announced.
The case arose after the memorial to the women of the Second World War in Whitehall was vandalised with the words "F*** Tory scum" during an anti-austerity protest.
The Twitter libel case - dubbed 'Twibel' by media pundits - will be significant to future defamation cases sparked by social media activity.
Monroe's lawyer told the High Court that Hopkins' tweets to Monroe - apparently in a case of mistaken identity - amounted to an allegation that would "inevitably cause serious damage to reputation".
It is believed that Hopkins had mistaken Monroe for New Statesman columnist Laurie Penny, who had tweeted that she didn't "have a problem" with the graffiti.
The judge heard it was a "widely published allegation" that Monroe had "either vandalised a war memorial or approved of such an act".
Jonathan Price, for Hopkins, argued: "This relatively trivial dispute arose and was resolved on Twitter in a period of several hours".
He asserted "no lasting harm, and certainly no serious harm" to Monroe's reputation resulted from it.
But Mr Justice Warby ruled "whilst the claimant may not have proved that her reputation suffered gravely, I am satisfied that she has established that the publications complained of caused serious harm to her reputation".
He said their publication "not only caused Ms Monroe real and substantial distress, but also harm to her reputation which was serious".
The judge concluded: "Ms Monroe is entitled to fair and reasonable compensation, which I assess at £24,000."
At the time of the tweet, Monroe had demanded an apology and a £5,000 donation to a migrant charity from Hopkins in order to avoid a court case.
While Hopkins deleted her offending tweet, she failed to apologise and went on to post a second defamatory tweet again mentioning Monroe.
Following the court's decision, Monroe, who also campaigns over poverty issues, tweeted: "It"s taken 21 months but today the High Court ruled that Hopkins statements to/about me were defamatory. I sued her for libel. and I won."
She added: "I'll be writing a longer statement shortly, but for now, to everyone who told me I couldn't, wouldn't, shouldn't - I could, I would, I did."
Media lawyer Mark Stephens said: "Mr Justice Warby has now set a tariff at £24,000 for Twibel cases. This is a level which will undoubtedly encourage more claims.
"People now need to be careful with their tweets - don't tweet now and repent at leisure."
It is not the first libel suit Hopkins has been involved in recently.
In December, Hopkins apologised to a British Muslim family over a Mail Online column in which she accused them of being extremists after they were refused entry to the US for a trip to Disneyland.
The newspaper was ordered to pay the family £150,000 in libel damages.
The Independent Press Standards Organisation previously rejected complaints over an article Hopkins had written for her former employer - The Sun - comparing migrants to "cockroaches".