LONDON, October 21, 2011 - The 22-year-old world number three -- widely regarded as golf's most talented youngster -- has split with Chandler's International Sports Management (ISM) firm after a four-year association, an ISM statement said.
The surprise move comes after a stellar year for McIlroy which saw the Northern Irish youngster land his first Major.
McIlroy said he was leaving ISM to join Dublin-based Horizon to help further his career. He joins fellow US Open champion Graeme McDowell at Horizon.
"I am now keen to move onto the next stage of my career and I feel this will be facilitated by a fresh view and a new structure around me," McIlroy said in a statement.
"Therefore I am delighted to be joining Horizon and I look forward to working with my new team.
"I would like to sincerely thank Andrew 'Chubby' Chandler and his team for their guidance, representation and management over the past four years since turning pro.
"Chubby and his team have played a very important role in my success to date. I have made great progress under their management and for that I will always be grateful."
Chandler, who also manages Lee Westwood, Open champion Darren Clarke and Masters winner Charl Schwartzel, was philosophical about the split.
"Onward and upwards," he said in a statement. "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.
"Under our management he has grown into an international figure and he leaves us as a major champion."