The transfer involves Freddie Burns moving in the other direction to Bath after making almost 65 appearances for the Tigers during a two-and-a-half-year spell.
Ford came through Leicester's academy in 2009 and four years later, after winning the Anglo-Welsh Cup and Aviva Premiership title, joined Bath.
Tigers head coach Aaron Mauger said: "We are absolutely delighted to be able to confirm the signing of George Ford, a player we obviously know well from his time here in the academy and as a young man making the breakthrough into senior rugby. He has become one of the leading players in his position in Europe and is still a young man with a lot of rugby ahead him. We look forward to his return to Welford Road in the summer.
"While delighted to be able to bring in George, we are disappointed to lose Freddie who has been an outstanding player for us in the last three years. Freddie has bought totally into the Tigers ethos in his time here and he is a popular member of the squad with the players and supporters.
"Freddie has made a significant contribution on and off the field here and we look forward to him continuing to play a prominent role with us in the remainder of the season while wishing him well when he moves to Bath in the summer."
Ford, who reached the European Challenge Cup final and Premiership final in 2014 and 2015 respectively with Bath, has been capped 32 times for England.