He was educated at Edinburgh High School on Calton Hill then articled as an architect, training under Patrick Wilson from 1844 to 1849.
He lived with McNeill at Colonsay House for some time and may have been involved in the relocation of the Riasg Buidhe Cross to the garden there.
He returned to Colonsay many times, presumably carrying out research for his book, The Battle of Tofrek ... under Major Gen. Sir John C. McNeil VC, KCB (Edinburgh 1888) and in 1882/3 excavated a Viking burial site at Kiloran Bay with Sir Malcolm.
Also in 1883 he excavated at Restenneth Priory with Dr John Stuart and also recorded the Corsehope Rings in Midlothian.
Galloway is thought to have moved permanently to Whithorn, living at 87 George Street but the Valuation rolls for 1885-8 suggest he was neither a proprietor nor a tenant there.
During this same period he assisted the architects MacGibbon & Ross in their survey of traditional architecture in south-west Scotland.
She sold his artefacts, photographic plates and rubbings (of Pictish stones) to the Society of Antiquaries.