Monroe sued Hopkins after she posted a tweet suggesting that the food blogger had taken part in or condoned the defacement of a war memorial.
And a judge ruled that the tweet had caused "serious harm" to her reputation, ordering Hopkins to pay damages.
After the result, Monroe 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."
The case arose after a memorial to the women of the Second World War in Whitehall was daubed with the words "F*** Tory scum" during an anti-austerity demonstration.
Monroe – who also campaigns against poverty – sued Hopkins over what her lawyer described as a "widely published allegation" that she had "either vandalised a war memorial or approved of such an act", an allegation that would "inevitably cause serious damage to reputation".
It"s taken 21 months— ❄Jack Monrowflake (@MxJackMonroe) March 10, 2017
but today the High Court ruled
that Hopkins statements to/about me were defamatory.
I sued her for libel.
and I won.
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.— ❄Jack Monrowflake (@MxJackMonroe) March 10, 2017
Hopkins’ lawyer - Jonathan Price – argued the case was a "relatively trivial dispute arose and was resolved on Twitter in a period of several hours".
He said "no lasting harm, and certainly no serious harm" to Monroe's reputation resulted from it and said that Hopkins had "mistakenly" used Monroe's Twitter handle instead of that of another columnist who had tweeted about the war memorial incident.
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."