Tsimikas agreed a five-year deal when he joined the Reds from Olympiakos in 2020, but the length of his new contract has not been disclosed.
"I feel very glad to be here to extend my contract. I feel like all the sacrifices I did and other things, the work I put in, everything pays off," Tsimikas told Liverpool's website.
"But this keeps me fully motivated for the rest. As I've said in many, many interviews, this team has many, many things to achieve all together and I wanted to be from the first minute a part of it."
Largely deputising for Liverpool's first choice left-back Andrew Robertson, Greece international Tsimikas has made 63 appearances and provided 12 assists since arriving at Anfield in an £11 million deal.
He has one Premier League appearance this season as a substitute against Bournemouth in August and started last week's Europa League win against LASK in Austria.
