Kostas Tsimikas was born on 12 May 1996 in Thessaloniki, Greece, and began his footballing journey at his local village club in Lefkonas before moving to AS Neapoli Thessaloniki at the age of 14. He turned professional with Olympiacos, where he won two Super League Greece titles, and developed further through loan spells at Danish side Esbjerg and Dutch club Willem II — the latter earning him the Eredivisie Rookie of the Month award in March 2018 after a standout season in which he scored five goals.
Tsimikas joined Liverpool in August 2020 for a reported fee of £11.75 million, becoming only the second Greek player in the club's history. His most memorable moment in a Liverpool shirt came in the 2022 FA Cup final against Chelsea, when he entered as a substitute late in extra time and scored the decisive penalty in a 6–5 shoot-out victory. He also played a key role in the 2024 EFL Cup final, assisting Virgil van Dijk's winning goal, and in April 2025 became the first Greek footballer to win the Premier League.
An attacking-minded left-back with a strong delivery from set pieces, Tsimikas is now on a season-long loan at Serie A club Roma for the 2025–26 campaign. Internationally, he made his senior debut for Greece in October 2018 and has represented his country in competitive fixtures including the 2026 FIFA World Cup Qualifiers, scoring his first international goal against Scotland in October 2025.