The 19-year-old, who spent two loan stints at Ewood Park last season, has been welcomed back by manager Gary Bowyer.
"First of all we've got to thank Chelsea once again, because they've been more than accommodating," Bowyer told the club's official website.
"With the new manager coming in, we were waiting to see if Todd was going to be part of his plans, but they see the advantage of him coming out and playing in the Championship again for a full season.
"Todd kicked on massively when he came and joined us last time. On the back of his performances here, he earned himself a new contract at Chelsea and rightly so."
The Blues have given Blackburn permission to play Kane in the FA Cup and the Capital One Cup.