Seguier was the eldest daughter of Anthony Stewart, 1773–1846, a portrait and miniature painter from Crieff in Perthshire and of Janet Weir whose father, Alexander Weir, was also a painter.[1][2] Their father taught both Margaret and her younger sister, Grace Campbell Stewart, to paint.[1][2] Margaret is praised in contemporary accounts for her portrait miniatures but no artistic record or specific attributions exist.[2] Margaret married John Seguier, 1785–1856, who was a picture restorer and supintendent at the British Institution. They had a son, Peter Seguier who became a successful author, writing A Critical and Commercial Dictionary of the Work of Painters.[1]