The Sweden international leaves Manchester City having failed to break into the Etihad Stadium first-team and has now agreed a short-term move to Scotland
The Scottish champions attempted to sign the 22-year-old on transfer deadline day but failed to file the relevant paperwork in time, but the Scottish Football Association subsequently appealed to Fifa on the club’s behalf in a bid to get the deal ratified.
And Celtic have now confirmed the signing of the Sweden international, who has struggled to nail down a spot in City’s starting XI in recent seasons.
Guidetti joined Stoke on loan in January, but signed a new contract at City in 2012, which ties him to the club until 2015.
The 22-year-old becomes Celtic's second signing in quick succession, with Serbian striker Stefan Scepovic joining the club for €2.8 million on Monday.