The 24-year-old becomes the Premier League champions’ first new signing of the summer.
Liverpool have made their first signing of the summer with the £11.75m ($15m) arrival of Greece defender Kostas Tsimikas from Olympiacos.
The 24-year-old, who has been given the number 21 shirt at Anfield after signing a five-year contract, will provide competition for Scotland international Andy Robertson in the left-back position.
Robertson did not face any natural competition for his starting place last season, with veteran James Milner filling in when required.
Tsimikas is a product of the Olympiacos youth academy and featured 46 times for the Pireaus side during the 2019-20 campaign, scoring seven goals.
The Reds turned their attentions to the Greece international after failing to agree terms with Norwich City over a deal for 22-year-old Jamal Lewis.
The Canaries turned down a £10m ($13m) bid from Liverpool for Lewis last week, and that ultimately persuaded Jurgen Klopp’s recruitment team to seal a deal for Tsimikas instead.
Speaking about the transfer, Liverpool boss Klopp said: “We have watched Kostas for a long time and are really happy that he has joined us. It’s the perfect news before we come back together very soon.
“He is a very good footballer with an attitude to win and to compete, and I really like his mentality. It fits perfectly with the mood and the desire we have in our dressing room already.
“He has showed already at a young age he can experience football in a different country and do well – and he has been a big part of the success Olympiacos has had to win their title this season and in their European campaigns.
“Kostas knows from personal experience what is required to challenge and succeed domestically and in the Champions League, and he is ambitious for more – just like us.
“He has come up against some very tough opponents in the past couple of seasons and done well and we know he relishes the challenge, which is perfect for us. For that reason we are delighted to know we’ll have him with us for the years ahead. I’m so pleased.”
Tsimikas has set his sights on winning silverware after joining what he says is “the biggest club in the world”.
“I’m very happy, I’m very proud to be here,” he told Liverpool’s website. “For me, [it’s] the biggest club in the world. It’s an honour to be here and I will give my best.
“The league here, I like a lot. I watch it on the TV and it was always one dream I had from when I was a kid to come to play in this league and to come through.
“With a lot of work and focus on what I do and what the coach wants, and every day working hard in training, I can be on the highest level.
“[I want] to achieve [our] goals. To win the league again and also to win the Champions League.”
Prior to Tsimikas’ arrival Liverpool’s summer transfer activity had focused on outgoings, with Dejan Lovren moving to Zenit St Petersburg and Adam Lallana joining Brighton on a free transfer. Nathaniel Clyne and Andy Lonergan have also been released.
