Neil Lennon will be in the Celtic dugout for Wednesday's trip to face Hearts and the rest of the season following Brendan Rodgers' sudden departure to Leicester.
Lennon has been installed as manager with John Kennedy his assistant and Damien Duff promoted to first-team coach after a short stint in charge of the reserves.
The former Celtic captain's extraordinary return capped off a whirlwind 12 hours after it emerged Celtic had "very reluctantly" given Rodgers permission to speak to Leicester.
Lennon won three league titles and two Scottish Cups in just over four years as Celtic manager after taking over from Tony Mowbray, initially on a temporary basis, in March 2010.
He said: "I am absolutely delighted to be named manager of Celtic again. This is a club which has been such a huge part of my life already and it is an honour to be asked to return.
"I have given everything to Celtic as a player and manager already in my career and I am ready to do the same again. I will be doing all I can to continue the great work that has gone on in recent years.
"I am delighted that John Kennedy and Damien Duff have agreed to be part of my team. John will allow us to have important continuity and Damien will bring real knowledge and experience to the first-team squad.
"I am returning to one of the biggest and best clubs in world football and I can't wait to get started."
Rodgers did not give much away over his reasons for departing Celtic in a statement on the club's official website, declaring he had been "living his dream" in almost three years in the role.
Chief executive Peter Lawwell said: "Brendan is a football manager of the highest quality and we are very disappointed to see him leave the club. This is an opportunity he wished to pursue and that is something we have to respect.
"He gave the club so much and has created so many wonderful memories for the club and our supporters. His achievements are historic."
Lawwell added: "In bringing Neil back to the club until the end of the season, we have appointed a man who knows what it means to be Celtic manager and someone who knows how to win.
"We know he has the commitment and desire needed to face the challenges ahead. We are delighted to also promote John Kennedy to assistant manager and bring Damien Duff into our first-team management group. This will bring vital continuity and allow us to build on Brendan's legacy.
"The club is in a great position on and off the field, and with Neil, John and Damien leading the first team, I am sure we can continue our success."
Lennon now has the chance to guide Celtic to a third consecutive treble and carry them further towards their target of sealing a record 10 titles in a row. The former Leicester player kicked off their current run of domination when he guided the Hoops to the championship in 2012.
Celtic are eight points clear of Rangers with the Betfred Cup already in the trophy room and with a William Hill Scottish Cup quarter-final against Hibernian, whom Lennon left in January, to come at Easter Road on Saturday.
