Francis is out of contract at cinch Stadium at Franklin's Gardens when this season ends and it has now been confirmed that he will join Bath.
The 31-year-old joined Saints from Super Rugby side the Blues in 2017 and has made 64 appearances for the club.
And Francis is now looking forward to his next challenge.
"With the players the club currently has and the ones that have been recruited, it is an exciting fresh start for me," Francis said.
"Every time I have played at The Rec you feel the buzz from the supporters.
"I can't wait to play in front of them and help the club progress."