The agency used social media to announce it had cut ties with the 21-year-old, but did not specify its reasons.
“IMG and Bernard Tomic have mutually ended our relationship,” IMG Tennis tweeted.
“We wish Bernard great success on and off the tennis court.” Reports in tennis publications said his off-court behaviour was behind the split.
Tomic had been with IMG since he was 13, before he won the boys’ titles at the 2008 Australian Open and 2009 US Open.
Their agreement spawned marketing deals potentially worth millions of dollars.
But in the space of two years, since reaching the fourth round of the 2012 Australian Open, Tomic has slipped from a career-high world ranking of 27 to a current 124.
His career has nosedived since withdrawing in the first round of the Australian Open against Rafael Nadal. He underwent double hip surgery shortly afterwards and then suffered a record 26-minute defeat on his comeback event at Miami.
Last year, his father John was banned from attending the French Open, even as a paying spectator, after he was charged with assaulting his son’s hitting partner, Frenchman Thomas Drouet in Madrid.
Drouet was left with a broken nose after a brawl broke out in front of the players’ hotel in the Spanish capital.
Tomic himself has also been in the headlines in recent years for the wrong reasons, including run-ins with police in his sports car.