The development of a considerable body of literature on British Sign Language (BSL) now permits analyzing and describing the sociolinguistic history of the language. An impressive amount of sociolinguistic information on BSL pertaining to the United Kingdom (UK) provides rich material for such analysis, but, until now, very little BSL research has focused on Northern Ireland. BSL is the first and preferred language of the deaf community in Northern Ireland, and has held that position since the nineteenth century. Despite this, almost no attention has been given to the sociolinguistic history of BSL in the region. The aim in this article is to fill the gap in knowledge by detailing, as far as possible, the sociolinguistic history of BSL in Northern Ireland rooted in British colonialism. The study shows how Protestant schools played an important role in the transmission of BSL across the island of Ireland. This research is, therefore, an attempt to place the study of BSL in Northern Ireland within the canon of literature on sign language.