The SPL champions turned to the Irish cider makers with their three-year association with Tennent's ending this summer.
The 'multi-million pound' three-year deal means Celtic will not share a sponsor with Glasgow rivals Rangers for the first time since 1999.
Commenting on the deal, Celtic chief executive Peter Lawwell said: "On behalf of everyone at Celtic, I am delighted to welcome Magners as the club's new shirt sponsor.
"This partnership is magnificent news, not only for Celtic but also for Scottish football. We are proud to be successfully leading Scottish football at home and in Europe.
"The desire of a brand with Magners' stature to support the club is a measure of how much positivity there is around Celtic in our 125th year.
"I look forward to a long and successful partnership with Magners and I'm sure every Celtic fan will welcome their support."
Tom McCusker, managing director of Magners, said: "There is a great fit with Celtic Football Club who also enjoy great success and popularity domestically and internationally.
"Everyone at Magners is looking forward to working with Celtic and its fans over the coming years in what promises to be an exciting time for the club and our brand."