Hardie specialized in the diseases of women and children, particularly those arising from climate. In 1893, he became president of the Medical Society of Queensland, which became a branch of the British Medical Association, the predecessor of the Australian Medical Association. On a visit to Europe in 1895 (with his wife and 3 children) he investigated Röntgen's work on x-rays but although he brought radiology equipment to Australia he did not pursue the work. During this trip he spent some time back in Moray with his ailing father, and also with his elder brother John's family at Westerton Farm, Pluscarden. In 1902 he built Firhall in Wickham Terrace where he resided and practised.