Ki will have to wait until January to make his Celtic debut
South Korean Ki Sung-Yong has signed a contract with Celtic "for up to four years", the club has confirmed.
The midfielder will join the Scottish Premier League leaders on 1 January after being granted a work permit.
Ki said: "I am absolutely delighted to sign for Celtic, a football club with a tremendous history and one which is known throughout the world."
Manager Tony Mowbray stressed: "We are sure he is a player who has the potential to make an impact at Celtic."
Ki, who leaves FC Seoul, is expected to join up with Mowbray's squad for training towards the end of December and could make his debut in the second Old Firm match of the season on 3 January.
He is a young man, but someone who we believe has the ability and character to do well for the club
Celtic manager Tony Mowbray
"I know that Celtic has some of the best supporters in the world and I will be doing all I can to show these fans what I can do and give everything as part of a team which will aim to achieve more and more success," Ki told Celtic's official website.
"When I lived in Australia, my football coach there was a Celtic supporter and, through him, I really became interested in the club.
"It is now a dream come true for me to join this great club - already, Celtic has shown me a tremendous welcome and I really do now feel part of the Celtic family.
"I look forward to teaming up with my new manager and team-mates and I will be working hard towards achieving all I can for Celtic."
Recently named Asian young player of the year, 20-year-old Ki featured in all of South Korea's qualification games en route to reaching next year's World Cup finals in South Africa and has scored four goals in 18 appearances for his country.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.