Relegated Rovers announce the signing of Republic of Ireland international on a four-year deal from the Magpies
The 25-year-old has penned a four-year deal with the Lancashire club and will wear the number nine shirt as manager Steve Kean aims to take the club back to the Premier League.
The club confirmed the signing on their official website. A statement on Monday read: "Blackburn Rovers have this evening completed the signing of Leon Best from Newcastle United.
"The 25-year-old striker makes the move from the North East to the North West for a fee of more than £3m, signing a four-year deal."
A Republic of Ireland international, Best began his professional career with Southampton and had a spell with Coventry City from 2007 to 2010.
He signed for Newcastle in 2010 for an undisclosed fee but his time with the Magpies was hindered by injuries.
The striker becomes Steve Kean's second signing of the season, with former Liverpool and Fulham midfielder Danny Murphy joining earlier in the summer.