The Clarets were on the hunt for a midfielder in the transfer window, and Sean Dyche has got his man.
Brownhill joins on a four-and-a-half year deal, which will see him play for the club during the best years of his career.
The club have an option to extend the deal by a year.
The 24-year-old is Burnley's first signing of the window.
"It's a really good feeling to be at Burnley. It's a big football club with a great fan base," said Brownhill on signing.
"Every time I've played here it's been nice to play at Turf Moor and I'm really excited.
"I can't wait to put on the shirt and play football. Whenever I get the chance, then I'll be ready to take it."