The "Harry Potter" scribe, 55, caught heat in June after making comments on Twitter that were deemed anti-trans in reference to an article referencing "people who menstruate."
"I’m sure there used to be a word for those people. Someone help me out. Wumben? Wimpund? Woomud?" she said online.
Since then, a number of stars associated with the author-turned-screenwriter have spoken out in opposition to Rowling's comments, including Redmayne, star of her "Fantastic Beasts" franchise, who voiced support for the transgender community in a statement to Variety.
"Respect for transgender people remains a cultural imperative, and over the years I have been trying to constantly educate myself,” he said. "This is an ongoing process. As someone who has worked with both J.K. Rowling and members of the trans community, I wanted to make it absolutely clear where I stand. I disagree with Jo’s comments."
The 38-year-old Oscar winner insisted that such "identities are valid," and stated that people within the transgender community are "are tired of this constant questioning of their identities, which all too often results in violence and abuse."
Now, Redmayne is sticking his neck out for the author.
Speaking to the Daily Mail, the actor condemned the "vitriol" aimed at her in recent months, calling the backlash "absolutely disgusting."
However, Redmayne maintained that the way transgender people are treated on social media is "equally disgusting."
"Similarly, there continues to be a hideous torrent of abuse towards trans people online and out in the world that is devastating," he said.
He also revealed that he's sent a note to Rowling amid the backlash, though the contents were not shared.
Redmayne is currently filming the third film in the "Fantastic Beasts" franchise, a spin-off of "Harry Potter" with a script co-written by Rowling. The franchise has drawn further controversy by its continued casting of Johnny Depp, who has been accused of beating his ex-wife Amber Heard.