Liverpool revealed earlier on Thursday they were in talks with the goalkeeper over a possible move to Anfield.
Lens are willing to let Itandje go after bringing in two new goalkeepers to the club over the summer.
The French club have announced that Itandje has tied up his move to Anfield as Liverpool were keen to get him signed up before the UEFA Champions League deadline.
The 24-year-old, who will provide cover for Jose Reina, was delighted to be making the move to Merseyside.
"I'm joining a great club, a Champions League finalist last year and previous winners, it's great," Itandje told Lens' official website.
"I've met great people (at Lens), an extraordinary public and rubbed shoulders with great players, frankly I'm leaving with a lot of emotion."