Pascal initially slammed Rowling in April for celebrating a UK Supreme Court ruling that stated trans women are not legally women under the Equality Act.
The actor, whose younger sister is trans, called Rowling's reaction "awful, disgusting" and "heinous LOSER behavior" on Instagram.
Pascal expressed that he agonized over whether his condemnation was "helping" but affirmed his desire to protect vulnerable people and his strong aversion to bullies.
Rowling's views on transgender people have made her a divisive figure, leading to public disagreements with the Harry Potter franchise's leading actors.