Liverpool have a catalogue of injuries at present, and Caulker will sign till the end of the season
Caulker will provide cover for the injured Martin Skrtel and Dejan Lovren after they succumbed to hamstring injuries – however the good news for Reds fans is that Kolo Toure and Mamadou Sakho will be fit to face Arsenal in their Premier League clash.
The 24-year-old was on loan at Southampton but that deal has been terminated to allow him to move to Anfield.
The paperwork was completed in time for him to be eligible to face Arsenal in the Premier League on Wednesday should manager Jurgen Klopp include him in the first team squad.
Caulker will be looking to kick-start his career after a promising start. The defender won his first England cap in 2012, and will look for some more stability after a series of loan moves during his time at former club Tottenham Hotspur.
Meanwhile, Southampton manager Ronald Koeman that are no replacements lined up to replace Caulker at St Marys.