The Northern Irishman has been with Chandler since he turned professional back in 2007, with the International Sports Management group that also has Open winner Darren Clarke, Lee Westwood and Ernie Els on their books.
However McIlroy has decided to go with a change of scene and will now join up with fellow Ulsterman Graeme McDowell at Dublin-based group Horizon.
It has been an amicable split and Chandler has insisted the future is still bright.
He said: "Onward and upwards. We have had a quite brilliant year. The company is growing and adapting to ensure it stays at the forefront of golf and the business of managing players. We wish Rory every success.
"It has been an honour representing Rory and we take great pride in the role ISM has played in guiding him successfully through his formative years as a professional golfer."