Moon won his first national title at the 1929 Open when he teamed up with Daphne Akhurst to win the Mixed Doubles championship. In 1934, he won the Mixed Doubles title for a second time with partner, Joan Hartigan.
In 1930, Gar Moon won the Australian Open's Men's Singles championship defeating Harry Hopman in the finals 6–3 6–1 6–3. In 1932 the native of Queensland completed the triple, capturing the Men's Doubles title with partner, Jack Crawford.
|Year||Championship||Opponent in Final||Score in Final|
|1930||Australian Championships||Harry Hopman||6–3, 6–1, 6–3|