"I consider him offensive and bigoted. But he has my full support to come to my country and be offensive and bigoted there."
The best-selling author said that Trump's freedom to make "bigoted" remarks, "protects my freedom to call him a bigot. His freedom guarantees mine".
She warned that attempts to repeal any of those freedoms, however well intentioned, means "we have set foot upon a road with only one destination".
Rowling explained that if she was to back a travel ban of Trump, because of his offensive comments, then she would have "no moral grounds on which to argue that those offended by feminism or the right for transgender rights or universal suffrage should not oppress campaigners for those causes".
"If you seek the removal of freedoms from an opponent simply on the grounds that they have offended you, you have crossed a line to stand along tyrants who imprison, torture and kill on exactly the same justification," she added.
This is not the first time that Rowling has lashed out at the Republican candidate.
In December, she described Trump as being worse than Lord Voldemort - the evil arch nemesis of Harry Potter in her fantasy franchise.
Rowling was responding to tweets which compared the billionaire to Voldemort after he proposed a ban on Muslims coming to America.
"How horrible," she wrote on Twitter. "Voldemort was nowhere near as bad."
The tweet was 'favourited' more than 38,000 times.
It wasn't long until the memes began either - with a picture of the Dark Lord wearing a wig, and a campaign poster for endorsing He-Who-Must-Not-Be-Named.
The following month, Rowling used another Harry Potter reference to attack Trump's campaign spokesperson after she asked if there were any "pure breeds" left.
Katrina Pierson had tweeted in 2012, during President Barack Obama's election campaign: "President Obama's dad born in Africa, Mitt Romney's dad born in Mexico. Any pure breeds left?"
The tweet sparked controversy after it resurfaced in January this year, garnering plenty of snarky tweets in response.
But the author blew them all out the water by responding "Death eaters walk among us."
The term Death Eaters is the name given to the followers of Lord Voldemort, the evil wizard in Rowling's Harry Potter series.
The Death Eaters roam the world pursuing their dark magic while casting fear and panic amongst ordinary wizarding folk all the while in servitude to Lord Voldemort.
They practiced the Dark Arts and thought anyone who was not "pure-blood" (a witch or wizard with no Muggles in their family) was inferior to them.