The nine-year-old arguably produced his best ever performance when second to Olympic Glory in the 2014 Lockinge Stakes at Newbury, a year in which he was fourth in both the Queen Anne Stakes and Queen Elizabeth II Stakes at Ascot.
At his best with a bit of juice in the ground, he was last seen finishing fourth to First Sitting in a Listed race at Goodwood in May, during which he picked up an injury.
A statement issued by owners Kennet Valley Thoroughbreds read: "His two runs as a nine-year-old proved that he still maintained his ability and love for racing but, after a minor injury sustained following his fourth in the Listed Matchbook Festival Stakes at Goodwood, the decision was made to retire him and to begin the early stages of retraining with Andrew's former assistant Chris Bonner and his wife, Claire.
"A great character who is an athlete through and through, we are hopeful to find him a new active career to pursue in the coming months.
"Tullius has been the most wonderful horse for a syndicate to own, along with Andrew Balding's team Park House Stables, his KVT owners wish him all the very best and to say thank you for all the incredible memories along the way."
Tullius won 11 of his 42 career starts, picking up over £500,000 in prize-money.