Warrington-born Brownhill made his first-team breakthrough at Preston after starting out in the youth set-up at Manchester United.
“I've been building myself up to this moment and I feel like it's the right time in my career to make that step up and show everyone I can play in the Premier League," said Brownhill.
“I really enjoyed my time at Bristol City. When I first joined we just survived relegation and since then we've got higher up the table. It's a great set of lads and a really good club.
“It was nice to get the experience back then and being the captain was special, but I think I'm ready now for the Premier League.
“From going to Preston to going out on loan, to going to Bristol City, it all happened at the right time and now is definitely the right time to make the step up into the Premier League, and especially at a club like Burnley."
He added: “I've watched over the years the way that Burnley play and it suits me that they are humble and hard-working, so I am really looking forward to it.
“I can't wait to get started. It's exciting and 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."