The 41-year-old passed away at his home after being discharged from hospital over the weekend to spend his last days with his family.
The Irish jockey was left stricken when he broke two vertebrae in 2013 as his horse Galaxy Rock fell at the first fence of the Fulke Walwyn Kim Muir Challenge Cup.
It is understood he suffered complications on Friday night before being transferred to University Hospital Limerick, before being discharged to be with his family.
McNamara enjoyed many of his big-race successes in the colours of owner JP McManus, riding Rith Dubh to victory in the famous green and gold colours in the 2002 National Hunt Chase at the Festival and partnering Spot Thedifference in the 2005 Cross Country Chase.
JT McNamara on board Galaxy Rock before the start of his Cheltenham race
He also wore McManus’ silks when riding Drombeag to win the 2007 Foxhunter Chase at Cheltenham and the owner’s racing manager, Frank Berry, hailed McNamara’s fortitude.
He said: “It’s so sad and all our thoughts go out to Caroline and the rest of the family.