The 34 year old found it hard to command a place in Rovers sides, him and Steve Kean had fallen out over a new deal which Roberts refused to sign.
It brings to an end Roberts' five-and-a-half-year stint with Blackburn where he made over 150 appearances, scoring 29 goals.
A statement on Rovers' official website read:"Jason Roberts has signed for Reading Football Club.
"The 34-year-old centre forward links up with the Championship club, with the terms of the transfer undisclosed."