Platt was born in Perth and had most of his brief education in New Zealand. He began his apprenticeship as an artist at the age of 20, when he worked and studied commercial art at Cedric Emanuel’s studio in Sydney, in the same building as Sydney Long’s studio. Cedric gave Austin lessons in etching at the Emanuel home in Dover Heights. Platt also studied at the Sydney Art School, the Royal Art Society, Maud Sherwood’s Sketch Club and at East Sydney Technical College, in such company as Long and Dattilo Rubbo. He went to Melbourne to sketch schools after the Collegiate Etching and Fine Arts Studio began to sell etchings of schools.