The legal abolition of slavery in Africa proved to be a protracted and ambiguous process. Laws against slavery were tentatively introduced, but were rarely consistently enforced, while forced labor schemes that shared a number of features in common with slavery persisted in the aftermath of legal abolition. Throughout this process, colonial rulers consistently sought to minimise the scope of their anti-slavery obligations by insisting that ‘domestic’ slavery was ‘benign’, and that their forced labor schemes should in no way be equated with slavery. At the same time, missionaries and colonial administrators were grappling with a series of analytical and institutional challenges around the question of ‘native’ marriage, which was similarly understood as a problem to be solved under the rubric of Europe’s self appointed ‘Civilising Mission’. This paper considers the various ways in which slavery and marriage were conceptualised and codified at a number of points in the history of colonial Africa, and seeks to understood both themes as different facets of a broader project of institutional codification, social engineering and ‘moral education’. The equation linking slavery and marriage in Africa was never straight-forward or uncontested, yet there was nonetheless a brief window in the early 1950s which resulted in a formal connection between the two being established, with ’servile marriage’ as slavery under international law during the twilight of colonial rule in Africa. By considering different approaches to this issue during the colonial period, this paper will in turn generate new insights and information from which to further assess recent and ongoing debates regarding the link between slavery and marriage in our own times.