Brown, 29, had long been expected to move to Ewood Park following his release from Doncaster, where he was named player of the year at the end of last season.
"As soon as I found out about the interest from Blackburn that's where I wanted to go," Brown told Blackburn's official website.
"It's a massive club with genuine ambitions for promotion and that is something that I wanted to be a part of and I can't wait to get started.
"I know a few of the lads here and they really rate the manager. I came to the training ground and had a look around and the staff made me feel very welcome. We have Premier League facilities here."
Brown, who began his career at Sunderland, has had previous spells at Norwich and Preston before sealing a move to Doncaster in 2011.
He scored nine goals in 43 appearances for Doncaster who were relegated from the Championship in May.