Born in Celle, she was the ninth of fifteen children born from the marriage of William the Younger, Duke of Brunswick-Lüneburg and Dorothea, Princess of Denmark. Most of the wedding guests stayed before and during the marriage feastivities at Heldburg Castle. In this occasion were used gilded state coaches, who belonged to the dowry of her mother Dorothea.
They are one of the oldest still functioning coaches in the world and currently displayed at the Veste Coburg.
John Casimir and Margaret had a happy marriage, but they had no children. Margaret returned to her homeland, Celle, where she died ten years later, aged 70.
She was buried in the Stadtkirche, Celle.