The 26-year-old has joined the Scottish champions on a four-year deal.
🇬🇷🍀 Introducing our new number 1️⃣…#WelcomeBarkas 💪
— Celtic Football Club (@CelticFC) July 30, 2020
Celtic will pay an initial €3.5m for Barkas with further add-ons to follow based on appearances.
Barkas has been capped ten times by Greece and in 111 games for AEK kept 61 clean sheets.
Vasilis is Celtic’s second Greek player after Georgios Samaras who scored 74 goals in five-and-a-half years at Parkhead.
The towering shot-stopper will replace Fraser Forster as Celtic number one.
Ajeti deal stalls
The 23-year-old has been in advanced talks to swap London for Glasgow next season.
But the Swiss international skipped his planned medical on Wednesday, asking for more time to consider his options.
A number of Premier League and European clubs are interested in Ajeti, which could scupper any move to Celtic.