For the 1926 National Jack Horner was owned by Mr. A.C. Schwartz who had paid 5,000 guineas for him a week beforehand. He had previously finished seventh in the 1925 running of the race when ridden by the American amateur Morgan de Witt Blair. In 1926, ridden by the Tasmanian jockey William Watkinson, Jack Horner started at odds of 25/1 in a field of thirty runners. The gelding took the lead in the closing stages and won by three lengths from Old Tay Bridge. Watkinson, who received £4,000 from the winning owner, was killed in a fall at Bogside Racecourse three weeks later. Jack Horner sustained a serious injury in training shortly afterwards and was retired without competing again.