The 'Loki' actor posted a picture of support for Watson's #HeForShe campaign on Twitter, reported Digital Spy.
"@EmWatson you are impeccable and extraordinary. I stand with you. I believe in gender equality. #heforshe," he wrote.
Watson, 24, recently launched the campaign for the United Nations in her role as Goodwill Ambassador for Women.
During a speech at the UN headquarters on September 20, Watson explained her 'uncomplicated' reasons for becoming a feminist and justified the 'unpopular word'.
The actress was subsequently threatened by apparent hackers in response to her speech, although this later turned out to be a hoax.