The Harry Potter creator has donated £1 million ($1.68 million) to help fund the campaign against Scottish independence.
Rowling has explained the reasons for making the donation in an article on her website.
The residents of Scotland will vote on Sept. 18 to decide whether to become an independent state. Rowling is English, but has a vote as a resident of Scotland.
Rowling, who has lived in Scotland for the past 21 years, first stated that she would vote against independence in 2012, but today’s donation marks her first active backing for the pro-union cause.