The house at its centre served for much of the twentieth century as a boarding school run by the Diocese of Clonfert, a fate common to many of Ireland's grander houses after independence, when maintaining such properties as private residences became untenable for their owners.

The demesne originally passed through the hands of the Trench family, who were prominent in Galway and further afield during the eighteenth and nineteenth centuries. The earls of Clancarty, a title held by the Trench family, were associated with the estate during its period of greatest influence. Country houses of this type typically comprised not just the main residence but an ensemble of ancillary structures, walled gardens, gate lodges, and designed parkland, all of which combined to project the social and economic standing of the landowning family. At Garbally, traces of this landscape still survive within the demesne grounds, even as the house itself has taken on successive institutional roles over the decades.