Longworth attended Sydney Grammar School where he excelled in athletics, swimming and rugby union. In January 1911, he won the 1320-yard freestyle in world record time at Australian Championship by 30 yards. He defeated Cecil Healy and Frank Beaurepaire. In 1912, he won all the New South Wales and Australian freestyle championships from 100 yards to one mile. In 1912, he qualified for the final of the 100-metre freestyle, as well as for the semifinals of the 1500-metre freestyle, but due to illness he was unable to continue competing.