The 30-year-old defender, who arrived in a reported £4.2million deal from FC Augsburg, claimed that he is honoured and has realised his dream by signing for the Reds.
He told the club's official website: "I'm really honoured to be part of this amazing club, this amazing team.
"It's hard to put it into words, because it's been a dream of mine for 22 years to come to the Premier League and be a part of this amazing club, Liverpool.
"I mean the history…how many trophies they've won. Then what kind of names have been here in Melwood and at Anfield Road – that I can be a part of this club…I can't describe it, it's something special.
"I'm privileged to be here."