The 25-year-old has been training with the Reds after undergoing a medical early this week.
Cissokho told the club's website: "I feel extremely proud to be here and I'm proud of all the hard work I've put in so far throughout my career.
"I've always dreamt of one day signing for a really legendary club. I've been lucky enough to play for a few top sides and so to now get the chance to play for a club like Liverpool, it's just fantastic.
"It's really pleasing when a club like Liverpool shows interest in you, and when that interest becomes more serious, you really can't wait for the move to go through.
"Now that the transfer has been completed, I'm really happy.
"I hope to feature in as many games as possible. I know it's going to be quite tough and I need to get to work as soon as possible as pre-season is over and we are into the league programme."
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